Evaluating the sources you find is a crucial step in the process of library research. The questions you ask about books, periodical articles, or multimedia sources are similar whether you're looking at a citation to the item or have the item in hand.
Critically Analyzing Information Sources lists some of the critical questions you should ask when you consider the appropriateness of a particular book, article, media resource, or Web site for your research.
Distinguishing Scholarly Journals from Other Periodicals shows how to evaluate periodicals by looking at their format, intended audience, and appearance.
Five Criteria for Evaluating Web Sites offers a table of suggestions.
For additional suggestions specific to Web sites, see Evaluating Web Sites: Criteria and Tools.