"There are some actions that can almost unquestionably be labeled plagiarism. Some of these include buying, stealing, or borrowing a paper (including, of course, copying an entire paper or article from the Web); hiring someone to write your paper for you; and copying large sections of text from a source without quotation marks or proper citation.
But then there are actions that are usually in more of a gray area. Some of these include using the words of a source too closely when paraphrasing (where quotation marks should have been used) or building on someone's ideas without citing their spoken or written work."
(From Is It Plagiarism Yet? by the Purdue Online Writing Lab.)
More information is available at Avoiding Plagiarism from the Purdue Online Writing Lab.
Citing the work that supports your research is both an ethical issue and a legal issue.
The ethics of citing is based on the scholarly tradition of giving credit for information and ideas that are not one's own. Science has a long tradition of acknowledging priority through citations. You have the ethical responsibility to cite all works that were used to support your research, to give credit to the earlier work and to provide a clear path for those who follow in your footsteps.
As so eloquently expressed by Isaac Newton in a letter to Robert Hooke in 1675 (Merton 1965):
If I have seen further it is by standing on ye sholders of Giants.
The legal issues of citing one's sources are codified in Copyrights, Title 17 of the U.S. Code, which describes the legal protections of authors' and creators' intellectual property rights.
[Merton, RK. 2006. On the shoulders of giants: a Shandean postscript. New York: The Free Press. p. 31]
AMA Style Guide (from University of Washington)
This guide is based on the AMA manual of style: guide for authors and editors, 10th ed. [Print copy of complete guide available in the Reference Collection Ref R119 .A533 2007]
Examples using AMA style:
Journal Article - in print
Raux H, Coulon P, Lafay F, Flamand A. Monoclonal antibodies which recognize the acidic configuration of the rabies glycoprotein at the surface of the virion can be neutralizing. Virology. 1995;210(2):400-408.
Journal Article - on the Web
Kapur VK, Obstructive sleep apnea: diagnosis, epidemiology, and economics. Respir Care. 2010;55(9):1155-1167. http://www.rcjournal.com/contents/09.10/09.10.1155.pdf Accessed November 8, 2011.
Shepard TH. Catalog of Teratogenic Agents.7th ed. Baltimore, MD: Johns Hopkins University Press; 1992.
Book Chapter - in an edited book
Degner LF, McWilliams ME. Challenges in conducting cross-national nursing research. In: Fitzpatrick JJ, Stevenson JS, Polis NS, eds. Nursing Research and its Utilization: International State of the Science. New York, NY: Springer; 1994:211-215.
Endnote is an application that imports citations from your searches in web databases and helps you organize your references. It works with Microsoft Word helping you create in-text citations, footnotes, and bibliographies.
EndNote Basic (formerly EndNote Web) is an online program that helps you organize references and create properly formatted bibliographies. This is a separate program from the desktop version of EndNote. It is a free version of EndNote available for institutions which subscribe to ISI Databases, like Web of Science.
Mendeley allows you to share references with others or to maintain a private library. Mendeley collections can be exported to Endnote, CiteULike, or Zotero libraries. Mendeley works with Word 2008 and OpenOffice to insert citations into your documents. It enables you to extract citation information from downloaded pdfs.
Zotero is a free Web application that you can also download to your computer. The library you create on the Web will sync with your desktop Zotero library. This software has advanced significantly in the last few years and is definitely worth trying. Zotero works with Word and OpenOffice after you have downloaded the plug-ins to insert citations into your document and generate a bibliography.