Even if you just used a particular book or web site for background research, you should include it in your Works Cited page.
HOW TO CITE: COMPOSITION OF A CITATION
Different elements of a citation are required for each of the various types of resources you use. The citation style you use (MLA, APA, Chicago, etc.) dictates what is required and how it is formatted, but basic citation elements remain fairly consistent across citation styles.
For books: author, title, publisher, place of publication, and publication date.
For articles: author, date, article title, journal title, journal volume and issue, and page numbers.
HOW TO CITE: CITATION STYLE GUIDES