Research includes reading the work of others who came before you in order to understand where your own work fits in the ongoing conversation of scholarship.
You will often need to refer to these articles, books, and other sources in writing assignments, longer documents like senior reports, theses and dissertations, and anything you're submitting for publication. When doing so, it's important to understand how a citation works within your paper.
One citation is really two parts:
Did you read the research of others when writing your own paper?
When you are informed by other researchers (which can include yourself!), you must cite the original authors of that work—in the text where the work appears and the corresponding full citation in the list of references—for two main reasons:
You do not need to include a citation for the following:
A reference or footnote in a document to a book, a magazine or journal article, or another source. It contains all the information necessary to identify and locate the work, including author, title, publisher, date, volume, issue number, and pages.
A software program that helps collect, organize and cite bibliographic metadata for articles, books, websites, reports, and other items.
The exact formatting of a citation, usually based on discipline standards.
Rules for writing and presenting text written by a publisher or organization in a particular discipline to establish uniform practices for all documents produced by that publisher or within that discipline.
Adapted from: Library Glossary (Benedictine University, via archive.org); Glossary of Library Terms (Davidson College); Cambridge Dictionary