What are the different types of citation styles?

There are many different citation styles used across different academic disciplines, but they fall into three basic approaches to citation:

Parenthetical citations: Including identifying details of the source in parentheses—usually the author’s last name and the publication date, plus a page number if available (author-date). The publication date is occasionally omitted (author-page).
Numerical citations: Including a number in brackets or superscript, corresponding to an entry in your numbered reference list.
Note citations: Including a full citation in a footnote or endnote, which is indicated in the text with a superscript number or symbol.

Frequently asked questions: Citing sources

What are scientific citation styles?: A scientific citation style is a system of source citation that is used in scientific disciplines. Some commonly used scientific citation styles are:

Chicago author-date, CSE, and Harvard, used across various sciences

ACS, used in chemistry

AMA, NLM, and Vancouver, used in medicine and related disciplines

AAA, APA, and ASA, commonly used in the social sciences
Is a source annotation the same thing as an abstract?: A source annotation in an annotated bibliography fulfills a similar purpose to an abstract: they’re both intended to summarize the approach and key points of a source.

However, an annotation may also evaluate the source, discussing the validity and effectiveness of its arguments. Even if your annotation is purely descriptive, you may have a different perspective on the source from the author and highlight different key points.

You should never just copy text from the abstract for your annotation, as doing so constitutes plagiarism.
Can I cite Wikipedia in my paper?: Most academics agree that you shouldn’t cite Wikipedia as a source in your academic writing, and universities often have rules against doing so.

This is partly because of concerns about its reliability, and partly because it’s a tertiary source. Tertiary sources are things like encyclopedias and databases that collect information from other sources rather than presenting their own evidence or analysis. Usually, only primary and secondary sources are cited in academic papers.
What are the main elements of a Wikipedia citation?: A Wikipedia citation usually includes the title of the article, “Wikipedia” and/or “Wikimedia Foundation,” the date the article was last updated, and the URL.

In APA Style, you’ll give the URL of the current revision of the article so that you’re sure the reader accesses the same version as you.
Is Wikipedia a reliable source for academic research?: There’s some disagreement about whether Wikipedia can be considered a reliable source. Because it can be edited by anyone, many people argue that it’s easy for misleading information to be added to an article without the reader knowing.

Others argue that because Wikipedia articles cite their sources, and because they are worked on by so many editors, misinformation is generally removed quickly.

However, most universities state that you shouldn’t cite Wikipedia in your writing.
When do I need to use a hanging indent?: Hanging indents are used in reference lists in various citation styles to allow the reader to easily distinguish between entries.

You should apply a hanging indent to your reference entries in APA, MLA, and Chicago style.
What is a hanging indent?: A hanging indent is used to indent all lines of a paragraph except the first.

When you create a hanging indent, the first line of the paragraph starts at the border. Each subsequent line is indented 0.5 inches (1.27 cm).
What are the main differences between APA and MLA?: APA and MLA style both use parenthetical in-text citations to cite sources and include a full list of references at the end, but they differ in other ways:

APA in-text citations include the author name, date, and page number (Taylor, 2018, p. 23), while MLA in-text citations include only the author name and page number (Taylor 23).

The APA reference list is titled “References,” while MLA’s version is called “Works Cited.”

The reference entries differ in terms of formatting and order of information.

APA requires a title page, while MLA requires a header instead.
How do I use parenthetical citations in Chicago style?: A parenthetical citation in Chicago author-date style includes the author’s last name, the publication date, and, if applicable, the relevant page number or page range in parentheses. Include a comma after the year, but not after the author’s name.

For example: (Swan 2003, 6)

To automatically generate accurate Chicago references, you can use Scribbr’s free Chicago reference generator.
What’s the difference between narrative and parenthetical citations in APA?: APA Style distinguishes between parenthetical and narrative citations.

In parenthetical citations, you include all relevant source information in parentheses at the end of the sentence or clause: “Parts of the human body reflect the principles of tensegrity (Levin, 2002).”

In narrative citations, you include the author’s name in the text itself, followed by the publication date in parentheses: “Levin (2002) argues that parts of the human body reflect the principles of tensegrity.”
How do I use parenthetical citations in MLA?: In a parenthetical citation in MLA style, include the author’s last name and the relevant page number or range in parentheses.

For example: (Eliot 21)
What is a parenthetical citation?: A parenthetical citation gives credit in parentheses to a source that you’re quoting or paraphrasing. It provides relevant information such as the author’s name, the publication date, and the page number(s) cited.

How you use parenthetical citations will depend on your chosen citation style. It will also depend on the type of source you are citing and the number of authors.
Can I use ibid. in APA Style?: APA does not permit the use of ibid. This is because APA in-text citations are parenthetical and there’s no need to shorten them further.
Can I use ibid. in Chicago style?: Ibid. may be used in Chicago footnotes or endnotes.

Write “Ibid.” alone when you are citing the same page number and source as the previous citation.

When you are citing the same source, but a different page number, use ibid. followed by a comma and the relevant page number(s). For example:

Ibid.

Ibid., 36.

Ibid., 40–42.
How do I use ibid. in my writing?: Only use ibid. if you are directing the reader to a previous full citation of a source.

Ibid. only refers to the previous citation. Therefore, you should only use ibid. directly after a citation that you want to repeat.
What does ibid. mean?: Ibid. is an abbreviation of the Latin “ibidem,” meaning “in the same place.” Ibid. is used in citations to direct the reader to the previous source.
How do I use signal phrases?: Signal phrases can be used in various ways and can be placed at the beginning, middle, or end of a sentence.

To use signal phrases effectively, include:

The name of the scholar(s) or study you’re referencing

An attributive tag such as “according to” or “argues that”

The quote or idea you want to include

Different citation styles require you to use specific verb tenses when using signal phrases.

APA Style requires you to use the past or present perfect tense when using signal phrases.

MLA and Chicago requires you to use the present tense when using signal phrases.
Why do I need to use signal phrases?: Signal phrases allow you to give credit for an idea or quote to its author or originator. This helps you to:

Establish the credentials of your sources

Display your depth of reading and understanding of the field

Position your own work in relation to other scholars

Avoid plagiarism
What is a signal phrase?: A signal phrase is a group of words that ascribes a quote or idea to an outside source.

Signal phrases distinguish the cited idea or argument from your own writing and introduce important information including the source of the material that you are quoting, paraphrasing, or summarizing. For example:

“Cognitive psychologist Steven Pinker (1994) insists that humans possess an innate faculty for comprehending grammar.”
How do I quote text that contains a citation?: If you’re quoting from a text that paraphrases or summarizes other sources and cites them in parentheses, APA and Chicago both recommend retaining the citations as part of the quote. However, MLA recommends omitting citations within a quote:

APA: Smith states that “the literature on this topic (Jones, 2015; Sill, 2019; Paulson, 2020) shows no clear consensus” (Smith, 2019, p. 4).

MLA: Smith states that “the literature on this topic shows no clear consensus” (Smith, 2019, p. 4).

Footnote or endnote numbers that appear within quoted text should be omitted in all styles.

If you want to cite an indirect source (one you’ve only seen quoted in another source), either locate the original source or use the phrase “as cited in” in your citation.
How many quotes should I use?: In scientific subjects, the information itself is more important than how it was expressed, so quoting should generally be kept to a minimum. In the arts and humanities, however, well-chosen quotes are often essential to a good paper.

In social sciences, it varies. If your research is mainly quantitative, you won’t include many quotes, but if it’s more qualitative, you may need to quote from the data you collected.

As a general guideline, quotes should take up no more than 5–10% of your paper. If in doubt, check with your instructor or supervisor how much quoting is appropriate in your field.
When should I quote instead of paraphrasing?: To present information from other sources in academic writing, it’s best to paraphrase in most cases. This shows that you’ve understood the ideas you’re discussing and incorporates them into your text smoothly.

It’s appropriate to quote when:

Changing the phrasing would distort the meaning of the original text

You want to discuss the author’s language choices (e.g., in literary analysis)

You’re presenting a precise definition

You’re looking in depth at a specific claim
How do I paraphrase effectively?: To paraphrase effectively, don’t just take the original sentence and swap out some of the words for synonyms. Instead, try:

Reformulating the sentence (e.g., change active to passive, or start from a different point)

Combining information from multiple sentences into one

Leaving out information from the original that isn’t relevant to your point

Using synonyms where they don’t distort the meaning

The main point is to ensure you don’t just copy the structure of the original text, but instead reformulate the idea in your own words.
What does “et al.” mean?: “Et al.” is an abbreviation of the Latin term “et alia,” which means “and others.” It’s used in source citations to save space when there are too many authors to name them all.

Guidelines for using “et al.” differ depending on the citation style you’re following:

APA

MLA

Chicago
How do I insert endnotes in Word?: To insert endnotes in Microsoft Word, follow the steps below:

Click on the spot in the text where you want the endnote to show up.

In the “References” tab at the top, select “Insert Endnote.”

Type whatever text you want into the endnote.
How do I convert footnotes to endnotes (or vice versa) in Word?: If you need to change the type of notes used in a Word document from footnotes to endnotes, or the other way around, follow these steps:

Open the “References” tab, and click the arrow in the bottom-right corner of the “Footnotes” section.

In the pop-up window, click on “Convert…”

Choose the option you need, and click “OK.”
How do I insert a footnote in Word?: To insert a footnote automatically in a Word document:

Click on the point in the text where the footnote should appear

Select the “References” tab at the top and then click on “Insert Footnote”

Type the text you want into the footnote that appears at the bottom of the page
What are footnotes used for?: Footnotes are notes indicated in your text with numbers and placed at the bottom of the page. They’re used to provide:

Citations (e.g., in Chicago notes and bibliography)

Additional information that would disrupt the flow of the main text

Be sparing in your use of footnotes (other than citation footnotes), and consider whether the information you’re adding is relevant for the reader.
What’s the difference between footnotes and endnotes?: Footnotes appear at the bottom of the page they refer to. This is convenient for the reader but may cause your text to look cluttered if there are a lot of footnotes.

Endnotes appear all together at the end of the whole text. This may be less convenient for the reader but reduces clutter.

Both footnotes and endnotes are used in the same way: to cite sources or add extra information. You should usually choose one or the other to use in your text, not both.
What is an in-text citation?: An in-text citation is an acknowledgement you include in your text whenever you quote or paraphrase a source. It usually gives the author’s last name, the year of publication, and the page number of the relevant text. In-text citations allow the reader to look up the full source information in your reference list and see your sources for themselves.
When do I need to cite myself?: If you are reusing content or data you used in a previous assignment, make sure to cite yourself. You can cite yourself just as you would cite any other source: simply follow the directions for that source type in the citation style you are using.

Keep in mind that reusing your previous work can be considered self-plagiarism, so make sure you ask your professor or consult your university’s handbook before doing so.
What makes a source credible?: A credible source should pass the CRAAP test and follow these guidelines:

The information should be up to date and current.

The author and publication should be a trusted authority on the subject you are researching.

The sources the author cited should be easy to find, clear, and unbiased.

For a web source, the URL and layout should signify that it is trustworthy.
What is the definition of peer review?: Peer review is a process of evaluating submissions to an academic journal. Utilizing rigorous criteria, a panel of reviewers in the same subject area decide whether to accept each submission for publication. For this reason, academic journals are often considered among the most credible sources you can use in a research project– provided that the journal itself is trustworthy and well-regarded.
What are examples of academic dishonesty?: Academic dishonesty can be intentional or unintentional, ranging from something as simple as claiming to have read something you didn’t to copying your neighbor’s answers on an exam.

You can commit academic dishonesty with the best of intentions, such as helping a friend cheat on a paper. Severe academic dishonesty can include buying a pre-written essay or the answers to a multiple-choice test, or falsifying a medical emergency to avoid taking a final exam.
What is academic dishonesty?: Academic dishonesty refers to deceitful or misleading behavior in an academic setting. Academic dishonesty can occur intentionally or unintentionally, and varies in severity.

It can encompass paying for a pre-written essay, cheating on an exam, or committing plagiarism. It can also include helping others cheat, copying a friend’s homework answers, or even pretending to be sick to miss an exam.

Academic dishonesty doesn’t just occur in a classroom setting, but also in research and other academic-adjacent fields.
How do I apply a hanging indent?: To apply a hanging indent to your reference list or Works Cited list in Word or Google Docs, follow the steps below.

Microsoft Word:

Highlight the whole list and right click to open the Paragraph options.

Under Indentation > Special, choose Hanging from the dropdown menu.

Set the indent to 0.5 inches or 1.27cm.

Google Docs:

Highlight the whole list and click on Format > Align and indent > Indentation options.

Under Special indent, choose Hanging from the dropdown menu.

Set the indent to 0.5 inches or 1.27cm.

When the hanging indent is applied, for each reference, every line except the first is indented. This helps the reader see where one entry ends and the next begins.
Do I need a citation when I quote or paraphrase an interview?: For a published interview (whether in video, audio, or print form), you should always include a citation, just as you would for any other source.

For an interview you conducted yourself, formally or informally, you often don’t need a citation and can just refer to it in the text or in a footnote, since the reader won’t be able to look them up anyway. MLA, however, still recommends including citations for your own interviews.
What are the main elements of an interview citation?: The main elements included in a newspaper interview citation across APA, MLA, and Chicago style are the names of the interviewer and interviewee, the interview title, the publication date, the name of the newspaper, and a URL (for online sources).

The information is presented differently in different citation styles. One key difference is that APA advises listing the interviewer in the author position, while MLA and Chicago advise listing the interviewee first.
What are the main elements of a newspaper article citation?: The elements included in a newspaper article citation across APA, MLA, and Chicago style are the author name, the article title, the publication date, the newspaper name, and the URL if the article was accessed online.

In APA and MLA, the page numbers of the article appear in place of the URL if the article was accessed in print. No page numbers are used in Chicago newspaper citations.
How do I cite a source with no title?: Untitled sources (e.g. some images) are usually cited using a short descriptive text in place of the title. In APA Style, this description appears in brackets: [Chair of stained oak]. In MLA and Chicago styles, no brackets are used: Chair of stained oak.

For social media posts, which are usually untitled, quote the initial words of the post in place of the title: the first 160 characters in Chicago, or the first 20 words in APA. E.g. Biden, J. [@JoeBiden]. “The American Rescue Plan means a $7,000 check for a single mom of four. It means more support to safely.”

MLA recommends quoting the full post for something short like a tweet, and just describing the post if it’s longer.
What are the main elements of an image citation?: The main elements included in image citations across APA, MLA, and Chicago style are the name of the image’s creator, the image title, the year (or more precise date) of publication, and details of the container in which the image was found (e.g. a museum, book, website).

In APA and Chicago style, it’s standard to also include a description of the image’s format (e.g. “Photograph” or “Oil on canvas”). This sort of information may be included in MLA too, but is not mandatory.
What are the main elements of a lecture citation?: The main elements included in a lecture citation across APA, MLA, and Chicago style are the name of the speaker, the lecture title, the date it took place, the course or event it was part of, and the institution it took place at.

For transcripts or recordings of lectures/speeches, other details like the URL, the name of the book or website, and the length of the recording may be included instead of information about the event and institution.
What are the main elements of a YouTube citation?: The main elements included in a YouTube video citation across APA, MLA, and Chicago style are the name of the author/uploader, the title of the video, the publication date, and the URL.

The format in which this information appears is different for each style.

All styles also recommend using timestamps as a locator in the in-text citation or Chicago footnote.
How do I write an annotation for a source?: Each annotation in an annotated bibliography is usually between 50 and 200 words long. Longer annotations may be divided into paragraphs.

The content of the annotation varies according to your assignment. An annotation can be descriptive, meaning it just describes the source objectively; evaluative, meaning it assesses its usefulness; or reflective, meaning it explains how the source will be used in your own research.
What types of sources should I use in an annotated bibliography?: Any credible sources on your topic can be included in an annotated bibliography. The exact sources you cover will vary depending on the assignment, but you should usually focus on collecting journal articles and scholarly books. When in doubt, utilize the CRAAP test!
What is an annotated bibliography?: An annotated bibliography is an assignment where you collect sources on a specific topic and write an annotation for each source. An annotation is a short text that describes and sometimes evaluates the source.
What are the main elements of a journal article citation?: The elements included in journal article citations across APA, MLA, and Chicago style are the name(s) of the author(s), the title of the article, the year of publication, the name of the journal, the volume and issue numbers, the page range of the article, and, when accessed online, the DOI or URL.

In MLA and Chicago style, you also include the specific month or season of publication alongside the year, when this information is available.
How do I cite a source with no author?: In APA, MLA, and Chicago style citations for sources that don’t list a specific author (e.g. many websites), you can usually list the organization responsible for the source as the author.

If the organization is the same as the website or publisher, you shouldn’t repeat it twice in your reference:

In APA and Chicago, omit the website or publisher name later in the reference.

In MLA, omit the author element at the start of the reference, and cite the source title instead.

If there’s no appropriate organization to list as author, you will usually have to begin the citation and reference entry with the title of the source instead.
What are the main elements of a website citation?: The main elements included in website citations across APA, MLA, and Chicago style are the author, the date of publication, the page title, the website name, and the URL. The information is presented differently in each style.
How do I cite a source with no page numbers?: When you want to cite a specific passage in a source without page numbers (e.g. an e-book or website), all the main citation styles recommend using an alternate locator in your in-text citation. You might use a heading or chapter number, e.g. (Smith, 2016, ch. 1)

In APA Style, you can count the paragraph numbers in a text to identify a location by paragraph number. MLA and Chicago recommend that you only use paragraph numbers if they’re explicitly marked in the text.

For audiovisual sources (e.g. videos), all styles recommend using a timestamp to show a specific point in the video when relevant.
When should I use “et al.” in citations?: The abbreviation “et al.” (Latin for “and others”) is used to shorten citations of sources with multiple authors.

“Et al.” is used in APA in-text citations of sources with 3+ authors, e.g. (Smith et al., 2019). It is not used in APA reference entries.

Use “et al.” for 3+ authors in MLA in-text citations and Works Cited entries.

Use “et al.” for 4+ authors in a Chicago in-text citation, and for 10+ authors in a Chicago bibliography entry.
Which citation style should I use?: Check if your university or course guidelines specify which citation style to use. If the choice is left up to you, consider which style is most commonly used in your field.

APA Style is the most popular citation style, widely used in the social and behavioral sciences.

MLA style is the second most popular, used mainly in the humanities.

Chicago notes and bibliography style is also popular in the humanities, especially history.

Chicago author-date style tends to be used in the sciences.

Other more specialized styles exist for certain fields, such as Bluebook and OSCOLA for law.

The most important thing is to choose one style and use it consistently throughout your text.
What are the main elements of a book citation?: The main elements included in all book citations across APA, MLA, and Chicago style are the author, the title, the year of publication, and the name of the publisher. A page number is also included in in-text citations to highlight the specific passage cited.

In Chicago style and in the 6th edition of APA Style, the location of the publisher is also included, e.g. London: Penguin.
What is a block quote?: A block quote is a long quote formatted as a separate “block” of text. Instead of using quotation marks, you place the quote on a new line, and indent the entire quote to mark it apart from your own words.

The rules for when to apply block quote formatting depend on the citation style:

APA block quotes are 40 words or longer.

MLA block quotes are more than 4 lines of prose or 3 lines of poetry.

Chicago block quotes are longer than 100 words.
When should I use quotes?: In academic writing, there are three main situations where quoting is the best choice:

To analyze the author’s language (e.g., in a literary analysis essay)

To give evidence from primary sources

To accurately present a precise definition or argument

Don’t overuse quotes; your own voice should be dominant. If you just want to provide information from a source, it’s usually better to paraphrase or summarize.
How do I cite a quote in academic writing?: Every time you quote a source, you must include a correctly formatted in-text citation. This looks slightly different depending on the citation style.

For example, a direct quote in APA is cited like this: “This is a quote” (Streefkerk, 2020, p. 5).

Every in-text citation should also correspond to a full reference at the end of your paper.
What is a quote?: A quote is an exact copy of someone else’s words, usually enclosed in quotation marks and credited to the original author or speaker.
How do I find the DOI of an article?: The DOI is usually clearly visible when you open a journal article on an academic database. It is often listed near the publication date, and includes “doi.org” or “DOI:”. If the database has a “cite this article” button, this should also produce a citation with the DOI included.

If you can’t find the DOI, you can search on Crossref using information like the author, the article title, and the journal name.
Why are DOIs important?: A DOI is a unique identifier for a digital document. DOIs are important in academic citation because they are more permanent than URLs, ensuring that your reader can reliably locate the source.

Journal articles and ebooks can often be found on multiple different websites and databases. The URL of the page where an article is hosted can be changed or removed over time, but a DOI is linked to the specific document and never changes.
When should I cite a chapter instead of the whole book?: When a book’s chapters are written by different authors, you should cite the specific chapter you are referring to.

When all the chapters are written by the same author (or group of authors), you should usually cite the entire book, but some styles include exceptions to this.

In APA Style, single-author books should always be cited as a whole, even if you only quote or paraphrase from one chapter.

In MLA Style, if a single-author book is a collection of stand-alone works (e.g. short stories), you should cite the individual work.

In Chicago Style, you may choose to cite a single chapter of a single-author book if you feel it is more appropriate than citing the whole book.
Is a newspaper article a primary or secondary source?: Articles in newspapers and magazines can be primary or secondary depending on the focus of your research.

In historical studies, old articles are used as primary sources that give direct evidence about the time period. In social and communication studies, articles are used as primary sources to analyze language and social relations (for example, by conducting content analysis or discourse analysis).

If you are not analyzing the article itself, but only using it for background information or facts about your topic, then the article is a secondary source.
Is a movie a primary or secondary source?: A fictional movie is usually a primary source. A documentary can be either primary or secondary depending on the context.

If you are directly analyzing some aspect of the movie itself – for example, the cinematography, narrative techniques, or social context – the movie is a primary source.

If you use the movie for background information or analysis about your topic – for example, to learn about a historical event or a scientific discovery – the movie is a secondary source.

Whether it’s primary or secondary, always properly cite the movie in the citation style you are using. Learn how to create an MLA movie citation or an APA movie citation.
How can you tell if a source is primary or secondary?: To determine if a source is primary or secondary, ask yourself:

Was the source created by someone directly involved in the events you’re studying (primary), or by another researcher (secondary)?

Does the source provide original information (primary), or does it summarize information from other sources (secondary)?

Are you directly analyzing the source itself (primary), or only using it for background information (secondary)?

Some types of source are nearly always primary: works of art and literature, raw statistical data, official documents and records, and personal communications (e.g. letters, interviews). If you use one of these in your research, it is probably a primary source.

Primary sources are often considered the most credible in terms of providing evidence for your argument, as they give you direct evidence of what you are researching. However, it’s up to you to ensure the information they provide is reliable and accurate.

Always make sure to properly cite your sources to avoid plagiarism.
What are some examples of secondary sources?: Common examples of secondary sources include academic books, journal articles, reviews, essays, and textbooks.

Anything that summarizes, evaluates or interprets primary sources can be a secondary source. If a source gives you an overview of background information or presents another researcher’s ideas on your topic, it is probably a secondary source.
What are some examples of primary sources?: Common examples of primary sources include interview transcripts, photographs, novels, paintings, films, historical documents, and official statistics.

Anything you directly analyze or use as first-hand evidence can be a primary source, including qualitative or quantitative data that you collected yourself.
Which citation software does Scribbr use?: The Scribbr Citation Generator is developed using the open-source Citation Style Language (CSL) project and Frank Bennett’s citeproc-js. It’s the same technology used by dozens of other popular citation tools, including Mendeley and Zotero.

You can find all the citation styles and locales used in the Scribbr Citation Generator in our publicly accessible repository on Github.

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Which citation software does Scribbr use?: The Scribbr Citation Generator is developed using the open-source Citation Style Language (CSL) project and Frank Bennett’s citeproc-js. It’s the same technology used by dozens of other popular citation tools, including Mendeley and Zotero.

You can find all the citation styles and locales used in the Scribbr Citation Generator in our publicly accessible repository on Github.