An index is a guide to the material published within other works, mostly periodicals. In a periodical index, you'll find every article for the periodicals and the period covered, typically listed by author, title, and subject. It will also include the source information, such as issue and page numbers.
Several common indexes will help if you're looking for general interest magazine or newspaper articles. The Readers' Guide to Periodical Literature is a good example and is available in print, on CD-ROM, and online. The printed version is a good choice, however, if you are doing any historical research. Begun in 1900, its older volumes are useful in locating popular press coverage of events happening at any time in the twentieth century-for example, articles about the bombing of Pearl Harbor published in the days after it happened.
Likewise, the New York Times index will help you track down that newspaper's coverage of events back to 1851. Another popular index is InfoTrac, a computerized resource that emphasizes materials written for a fairly general audience (though one version, the Expanded Academic Index, includes scholarly journals).
NewsBank, is an index to newspapers that draws on more than 500 local U.S. newspapers. Updated monthly, it is available both in print and on CD-ROM. Your library may also have an index to a local newspaper as well, which can help you track issues in your area. Some computerized indexes include downloadable and printable abstracts and full-text articles.
The Humanities Index, the Social Sciences Index, the General Science Index, the Business Periodicals Index, or PAIS International, an index focusing on public affairs, are aimed at more specialized audiences and provide more analysis than those found in popular magazines. The computerized Expanded Academic Index provides the same kind of coverage as the first three of these indexes. These tools index the most important scholarly journals in their fields, but they don't include obscure or highly specialized publications. The articles found in these indexes will be fairly long, include footnotes, and be based on and give detailed research information. These are the kinds of indexes you'll want to use for detailed research on social issues, literary criticism or science and medicine.