APA, MLA, Chicago and Harvard: choosing and using a citation style

Referencing exists to do one job: let a reader find exactly the source you used. Every rule in every style guide is downstream of that. Once you see citation as giving directions to a source rather than as arbitrary formatting, the conventions start to make sense — and it becomes obvious why a missing volume number matters and a missing full stop mostly does not.

That said, marks are awarded for consistency, so the conventions do matter. This guide covers what differs between the four styles you are most likely to be assigned, how to cite the awkward cases, and the specific errors that cost the most. Our citation generator will format individual references for you; this page explains what it is doing and when to override it.

The two families

Nearly every citation style belongs to one of two families, and knowing which one you are in tells you most of what you need.

Author–date (parenthetical) styles put the author's surname and the year in the running text: (Okonkwo, 2019). APA and Harvard work this way. They suit disciplines where how recent a source is carries information — the sciences, social sciences, medicine, education, business.

Author–page and note styles either give author and page without a date, as MLA does — (Okonkwo 143) — or move the citation into a footnote entirely, as Chicago's notes system does. These suit disciplines where you cite specific passages of specific texts and a work's date is less central: literature, history, philosophy, the arts.

The four styles in practice

APA (7th edition)

Published by the American Psychological Association and standard across psychology, education, nursing and much of the social sciences. Distinctive features: initials rather than full first names; sentence case for article and book titles but title case for journal names; the year immediately after the author; and DOIs presented as full https:// links.

APA 7 changed several things from APA 6 that still catch people out. Publisher locations are no longer required. Up to twenty authors are listed in the reference (APA 6 stopped at seven). In-text citations with three or more authors use "et al." from the first mention. And "Retrieved from" is no longer used before a URL unless you are including a retrieval date.

MLA (9th edition)

Published by the Modern Language Association, standard in literature, languages and cultural studies. In-text citations carry a page number and no date, because in literary study you are pointing at a passage.

MLA 9's important idea is the container. Rather than a separate template for each source type, MLA describes a source through nine ordered elements — author, title of source, title of container, contributors, version, number, publisher, publication date, location — and you fill in the ones that apply. An article sits in a journal; the journal may sit in a database. Each is a container, and you work outwards. This is why MLA handles unusual sources more gracefully than the template-based styles: there is no need for a rule about citing a podcast episode within a series within a platform.

Chicago (17th/18th edition)

Chicago offers two systems, and confusing them is the most common Chicago error. Notes and bibliography uses superscript numbers with footnotes or endnotes, and is standard in history and the humanities. Author–date uses parenthetical citations much like APA, and is used in some sciences. Your department will specify which; they are not interchangeable within one piece of work.

In the notes system, the first note for a source gives full details and subsequent notes are shortened to author surname, short title and page. Chicago also permits discursive footnotes — genuine commentary alongside the citation — which is part of why historians favour it.

Harvard

Harvard is the odd one out: it is not a single published standard but a family of author–date conventions, and individual universities publish their own Harvard guides that differ in real details — whether titles take single quotation marks, whether "pp." precedes page ranges, how to punctuate multiple authors.

The practical consequence: if you are told to use Harvard, find your own institution's Harvard guide and follow it. A generic Harvard formatter will get you close but will not match your department's expectations, and Harvard marking usually rewards internal consistency over conformity to any particular variant.

Citing awkward sources

Most citation difficulty comes from sources that lack the fields the template expects. The general principle across all styles: substitute the next most specific identifying element, and never invent one.

• No author. Move the title into the author position. Do not use "Anonymous" unless the work is genuinely credited that way. For organisational publications — a government report, a departmental web page — the organisation is the author: use "Department for Education" rather than treating it as authorless.
• No date. APA and Harvard use (n.d.). If a reader would need to know when you consulted an unstable page, add an access date.
• No page numbers (an ebook, a web page). MLA and Chicago accept a chapter, section heading or paragraph number. APA suggests a heading plus paragraph number for direct quotations.
• A source quoted inside another source. Cite the one you actually read: (Okonkwo, 2019, as cited in Silva, 2023). Only Silva goes in your reference list, because Okonkwo is not a source you can vouch for. Better still, find the original.
• Government and legal documents. These have their own conventions in every style, and legal citation in particular is a separate discipline. Statutes, cases and official reports usually need the jurisdiction and an official identifier rather than a publisher.
• Generative AI output. All four styles now address this, and all treat it as a citable source with the model and version named. But check your institution's academic integrity policy first — whether you may use it at all is a separate question from how to cite it, and citation does not confer permission.

The mistakes that actually cost marks

Markers rarely deduct for a misplaced comma. These are the errors that do damage:

1. In-text citations that do not match the reference list. Every in-text citation must have a corresponding entry, and every entry must be cited somewhere. Mismatches are the most commonly penalised referencing fault because they suggest the bibliography was assembled separately from the writing.
2. Mixing styles within one document. Usually a symptom of copying references from different sources without normalising them. Pick one style and apply it throughout, including to the awkward sources.
3. Quoting without a page reference. A direct quotation needs a locator in every style. This is the difference between a citation a reader can verify and one they cannot.
4. Paraphrasing without citing. Rewording someone's idea still requires attribution. Unattributed paraphrase is plagiarism in every academic integrity policy, and it is what most detected plagiarism actually consists of.
5. Trusting a generator's output unread. Automated tools — including ours — produce a reference from the fields you give them. If the metadata is wrong or incomplete, the reference is wrong. Always read the result against the source.

A workflow that avoids most of this

Referencing becomes painful when it is left until the end. A better sequence:

1. Confirm the required style before you start. Check the assignment brief, then your department's guide. If they conflict, ask.
2. Record full details when you first read a source — every field the style needs, plus the page you took each note from. Reconstructing this later is the single largest waste of time in academic writing.
3. Cite as you write, in the correct style, rather than marking places to fill in later.
4. Check the pair at the end: read your reference list against your in-text citations in both directions.
5. Verify one detail per reference against the source itself. A volume number, a page range, a year. This catches most transcription errors cheaply.

This guide describes the published conventions of each style in general terms. Style manuals are revised, and institutions publish their own variants — particularly for Harvard. Where your department's guide differs from anything here, follow your department. Found an error? Let us know.