Citation styles are standardised systems that prescribe how to format in-text citations and reference entries so that sources are credited consistently and can be retrieved reliably. The major styles — APA 7th edition, MLA 9th edition, the Chicago Manual of Style 17th edition, and Vancouver — share the same underlying data elements but differ in how those elements are ordered, punctuated and signalled in the text.
Choosing a style is rarely a free decision: each discipline has settled on conventions, and journals, publishers and institutions specify which to use. The skill is applying the chosen style consistently, not memorising all of them.
The four major styles at a glance
| Style | Typical disciplines | In-text format | End-of-text list |
|---|---|---|---|
| APA 7 | Psychology, education, social sciences | Author–date: (Author, Year) | References, alphabetical |
| MLA 9 | Humanities, languages, literature | Author–page: (Author 14) | Works Cited, alphabetical |
| Chicago 17 | History, arts, some social sciences | Notes-bibliography (footnotes) or author–date | Bibliography or References |
| Vancouver / ICMJE | Medicine, biomedical sciences | Numeric: [1] or superscript | References, by order of citation |
APA 7th edition
APA is an author–date style dominant in psychology and the social sciences. In-text citations carry the author surname and year, with a page number for direct quotations. The end list is titled “References”, alphabetised by surname, with a strong emphasis on the publication year because currency matters in empirical fields. DOIs are included as full https links.
MLA 9th edition
MLA serves the humanities, where the location of a phrase within a work often matters more than the year. Its in-text citation is author–page — (Author 14) — and the end list is titled “Works Cited”. MLA 9 organises an entry around a template of “core elements” (author, title of source, title of container, and so on), which makes it adaptable to non-traditional sources.
Chicago Manual of Style 17th edition
Chicago is distinctive for offering two complete systems:
- Notes–bibliography. Used in history and the arts. Citations appear as numbered footnotes or endnotes, with a full bibliography at the end. This suits narrative disciplines where discursive notes add value.
- Author–date. Used in the sciences and some social sciences, this variant works like APA — an in-text (Author Year) marker keyed to an alphabetical reference list.
The existence of two Chicago systems is the most common source of confusion; always confirm which one a publisher expects.
Vancouver and ICMJE
Vancouver is the numeric style of medicine and the biomedical sciences, aligned with the recommendations of the International Committee of Medical Journal Editors (ICMJE). Sources are numbered in order of first appearance and listed in that order. This keeps dense clinical text uncluttered — a paper may cite dozens of sources per page — at the cost of hiding authorship behind a number. The mechanics of numeric versus author–date markers are detailed in in-text citations versus the reference list.
Choosing the right style
The decision usually follows a simple hierarchy:
- Follow the journal or publisher first. Their author guidelines override personal preference.
- Then follow your discipline. Social sciences default to APA, humanities to MLA, history to Chicago notes-bibliography, medicine to Vancouver.
- Then follow your institution. A department or supervisor may mandate a house style.
- Apply it consistently. Mixing styles within one document is itself an error, regardless of which you choose.
Whatever style applies, the underlying data — author, year, title, container, persistent identifier — stays the same; only the presentation changes. Recording those elements accurately, and disambiguating authors with an ORCID iD, is what makes switching styles painless. This consistency also supports research integrity by keeping every claim traceable to a retrievable source. Practical help for applying a style is in our resources for authors.
Frequently asked questions
What is the difference between APA and MLA?
APA uses author–date in-text citations and is standard in the social sciences, emphasising the year of publication. MLA uses author–page citations and is standard in the humanities, emphasising the location of material within a source. Their end lists are “References” and “Works Cited” respectively.
Why does Chicago have two systems?
Chicago offers a notes-bibliography system, suited to history and the arts where footnotes carry discursive comment, and an author–date system suited to the sciences. The two serve different writing cultures, so always confirm which variant a publisher requires.
Which citation style should I use?
Use the style your target journal, publisher or institution specifies; if none is mandated, follow your discipline’s convention. The most important rule is to apply a single style consistently throughout the document.
Do all styles include a DOI?
The major styles all accommodate persistent identifiers such as DOIs, because they make references durable and retrievable. The exact placement and formatting differ by style. See the CASRAI dictionary for standardised term definitions.
