The bibliography — called “References” in APA style, “Works Cited” in MLA style, and “Bibliography” in Chicago style — is the final section of a research paper and lists every source cited in the text. Its purpose is transparency: it allows readers to locate, evaluate, and build on the sources the writer used. A well-formatted bibliography demonstrates scholarly rigor; a bibliography with missing entries, inconsistent formatting, or inaccurate information undermines the paper’s credibility regardless of the quality of the argument. This guide, part of iResearchNet’s How to Write a Research Paper series, covers the three citation styles most commonly required in U.S. higher education, the principles that govern all bibliography formatting, and the tools that make the process efficient and accurate.
General Principles
Despite their differences, all citation styles share several principles that students should internalize before learning any specific format.
Every in-text citation must have a corresponding bibliography entry, and every bibliography entry must be cited at least once in the text. Mismatches — a parenthetical citation that does not appear in the bibliography, or a bibliography entry for a source that is never cited — are among the most common formatting errors and are easy to catch during a systematic review.
Entries are listed alphabetically by the first element — typically the first author’s last name. When no author is identified, the entry is alphabetized by title (ignoring articles like “A,” “An,” and “The” at the beginning). Entries by the same author are ordered chronologically (oldest first in APA, by title in MLA).
Formatting must be consistent across all entries. If one journal article entry includes a DOI, all journal article entries that have DOIs must include them. If one book entry uses sentence-case capitalization for the title, all book entries must use sentence case. Inconsistency signals carelessness even when individual entries are correctly formatted.
Hanging indentation is used in all three major styles: the first line of each entry is flush with the left margin, and subsequent lines are indented one-half inch.
APA Style (7th Edition)
APA style is the standard citation format in psychology, education, nursing, social work, business, and most social sciences. The reference list is titled “References.”
In-Text Citations
APA uses author-date parenthetical citations: (Smith, 2023) for a paraphrase, (Smith, 2023, p. 47) for a direct quotation. Two authors are joined by an ampersand in parenthetical citations: (Smith & Jones, 2023). Three or more authors use the first author’s name followed by “et al.” from the first citation onward: (Smith et al., 2023).
Reference List Format
Journal article: Author, A. A., & Author, B. B. (Year). Title of article in sentence case. Title of Periodical in Title Case, Volume(Issue), Page–Page. https://doi.org/xxxxx
Book: Author, A. A. (Year). Title of book in sentence case (Edition, if not first). Publisher.
Edited book chapter: Author, A. A. (Year). Title of chapter. In B. B. Editor (Ed.), Title of book (pp. xx–xx). Publisher.
Website: Author or Organization. (Year, Month Day). Title of page in sentence case. Site Name. https://www.example.com/page
Key APA conventions: titles of articles and books use sentence case (only the first word, proper nouns, and the first word after a colon are capitalized); journal titles use title case and are italicized; DOIs are required for all sources that have them and are formatted as URLs (https://doi.org/xxxxx); publisher location is no longer included (7th edition change).
MLA Style (9th Edition)
MLA style is the standard citation format in English, comparative literature, foreign languages, and some humanities fields. The source list is titled “Works Cited.”
In-Text Citations
MLA uses author-page parenthetical citations: (Smith 47). No comma separates the author and page number. No “p.” precedes the page number. When the author’s name appears in the sentence, only the page number appears in parentheses: Smith argues that “…” (47).
Works Cited Format
MLA 9th edition uses a container-based model. Every source has core elements — Author, Title, Container (journal, website, anthology), Contributors, Version, Number, Publisher, Date, Location (pages, URL, DOI) — that are assembled in a consistent order regardless of source type.
Journal article: Author Last, First. “Title of Article.” Title of Journal, vol. #, no. #, Year, pp. xx–xx. Database Name, DOI or URL.
Book: Author Last, First. Title of Book. Publisher, Year.
Website: Author Last, First. “Title of Page.” Website Name, Publisher, Day Month Year, URL.
Key MLA conventions: titles of articles and chapters use quotation marks; titles of books, journals, and websites are italicized; all major words in titles are capitalized (title case); URLs are included but “https://” may be omitted; access dates are included when no publication date is available.
Chicago Style (17th Edition)
Chicago style is used in history, some social sciences, and publishing. It offers two citation systems: Notes-Bibliography (NB) and Author-Date (AD). The Notes-Bibliography system is standard in the humanities; the Author-Date system resembles APA and is used in some social sciences.
Notes-Bibliography System
Citations appear as numbered footnotes (or endnotes), with full bibliographic information in the first note and shortened form in subsequent notes. A bibliography at the end lists all cited sources.
First footnote (book):
- First Last, Title of Book (Place: Publisher, Year), page.
Subsequent footnote: 2. Last, Short Title, page.
Bibliography entry (book): Last, First. Title of Book. Place: Publisher, Year.
Bibliography entry (journal article): Last, First. “Title of Article.” Title of Journal Volume, no. Issue (Year): pages. DOI or URL.
Key Chicago conventions: the NB system supports discursive footnotes (analytical commentary alongside citations); bibliography entries use period-separated elements; publisher location is included (unlike APA 7th edition); journal article titles are in quotation marks with title case.
Author-Date System
The Author-Date system uses parenthetical citations (Smith 2023, 47) and a “References” list, similar to APA. It is less common in student papers but is used in some social science courses that follow Chicago rather than APA.
Using Citation Managers
Citation managers automate much of the formatting work and dramatically reduce the errors that manual formatting produces. Three tools dominate U.S. academic use.
Zotero is free, open-source, and available for all major platforms. It captures citation data from databases with a single browser click, stores and organizes sources, annotates PDFs, and generates formatted bibliographies in APA, MLA, Chicago, and thousands of other styles. Zotero integrates with Microsoft Word, Google Docs, and LibreOffice through plugins that insert citations and generate the bibliography automatically during drafting. Most U.S. university libraries offer free Zotero workshops.
Mendeley (Elsevier) is free for individual accounts and provides PDF annotation, citation management, and bibliography generation. EndNote (Clarivate) is the most feature-rich option but requires a paid license, available through some universities.
The key benefit of citation managers is not speed but accuracy. A citation manager that stores the bibliographic data correctly at the point of source capture will format that data correctly every time, in any style, without the manual errors that accumulate when students type reference entries by hand. Students should verify that the imported data is complete and correct (citation managers occasionally misread fields from database records) but should not format reference entries manually when a citation manager is available.
Common Bibliography Errors
Missing DOIs. APA 7th edition requires DOIs for all sources that have them. Many students omit DOIs because the database they used did not display them prominently. CrossRef provides a free DOI lookup tool that retrieves DOIs from article metadata.
Inconsistent formatting. Mixing APA and MLA conventions within the same bibliography — capitalizing some article titles in title case (MLA) and others in sentence case (APA), for instance — is more common than students realize and signals that the student has been copying formatting from multiple sources rather than applying a single style consistently.
Ghost entries. Including sources in the bibliography that are not cited in the text — often sources the student read but did not end up using — inflates the bibliography without supporting the argument. Every entry should correspond to at least one in-text citation.
Incomplete entries. Omitting required elements — a journal article without volume and issue numbers, a website without an access date (when required), or a book without a publisher — prevents the reader from locating the source, which defeats the bibliography’s purpose.
URL decay. URLs change and pages are removed. When a DOI is available, it should be used instead of a URL because DOIs are permanent identifiers that resolve to the current location of the article regardless of URL changes. For web sources without DOIs, the student should verify that each URL is functional before submission.
Frequently Asked Questions
Which citation style should I use?
The assignment or course syllabus specifies the required style. When no style is specified, the default depends on the discipline: APA for social sciences, health sciences, education, and business; MLA for English, literature, and languages; Chicago for history and some social sciences. When in doubt, ask the instructor.
How many sources should my bibliography include?
The number of sources depends on the assignment’s length, complexity, and requirements. A general guideline is one to two sources per page of text — a ten-page paper typically includes ten to twenty sources. Some assignments specify a minimum number. Quality consistently matters more than quantity: five carefully selected peer-reviewed sources contribute more than twenty superficially cited web pages.
Do I need to cite sources I read but did not quote or paraphrase?
If a source influenced your thinking or informed your argument — even if you did not quote or paraphrase it directly — it should generally be cited. However, sources that you read but that did not contribute to the paper should not appear in the bibliography. The bibliography lists sources that the paper actually uses, not everything the student read during the research phase.
Can a citation manager make mistakes?
Yes. Citation managers import bibliographic data from databases, and that data is occasionally incomplete or incorrectly formatted — a subtitle may be missing, an author’s name may be truncated, or the publication year may be wrong. Students should review every imported record for accuracy before generating the final bibliography. The citation manager handles formatting; the student is responsible for data accuracy.
Related Pages
- How to Write a Research Paper — Complete step-by-step guide
- How to Revise and Edit a Research Paper — Final review including citation verification
- How to Take Notes — Organizing sources during research
- How to Do Research — Finding and evaluating sources
- How to Do Library Research — Using databases and library resources