Peer-reviewed articles are written by experts and researchers who want to share their research with others in the field. These articles go through a long process of review by experts in the field before publication. Peer-reviewed articles are considered the best examples of research in a given field because of the standards and the long process of review that articles go through to determine the validity and credibility of the research.
Ulrich's Periodical Directory will tell you if a journal is peer-reviewed (refereed). Type in the journal's name and look in the "Refereed" field.
Watch the short tutorial below for more tips on identifying peer-reviewed articles.