Turnitin.com has some insight on why students plagiarize, types of plagiarism, and how to design assignments that discourage plagiarism.  They also sell software for plagiarism detection.

PAIRwise is a free, open-source software for plagiarism detection.

Plagiarism Detection Sites and Detecting Plagiarized Papers - Adapted from "Cheating 101: Paper Mills and You", a Teaching Effectiveness Seminar presentation by Margaret Fain and Peggy Bates, Kimbel Library, Coastal Carolina University.  Used by permission.

Strategies to Deter Plagiarism - Adapted from a newspaper article by Gary M. Galles, Professor of Economics, Pepperdine University.

Creating Successful Library Research Assignments - Used by permission of Merril-Cazier Library, Utah State University.

Integrity: Academic and Political; a Letter to My Students - Excellent essay by Bill Taylor, Professor of Political Science, Oakton Community College and chair of the Center for Academic Integrity.

The Importance of Writing - Essay on college writing and plagiarism by Louis Bloomfield, Professor of Physics, University of Virginia.