Books and periodicals are both sources of information. Books usually provide a general overview of a broad subject area or an in-depth look at several aspects of a subject.
Periodicals contain articles which have more focused and current information than books.
The articles can be in magazines, newspapers, serials, and journals. In order to find the articles, you need to use a periodical index. Periodical Indexes are searching tools to find articles by topic or subject. The indexes can be in print format or electronic format. They are the alphabetical listings of authors, titles, keywords, and subjects.