Here are a few useful sources for getting an overview of a topic before starting your research:
Sage Handbook of Social Work Research Ranging over local and international issues and exploring questions of theory and practice, this diverse study provides a comprehensive account of the state of the art of social work research.
Encyclopedia of Social Work online- 20th edition, 2008. From NASW, the National Association of Social Workers, the information on dozens of key topics is presented in the context of the issues and concerns of Social Workers.
Gale Virtual Reference Library online collection of dozens of encyclopedias, handbooks, and guides. From this site you can search all of them by key word, subject, and other ways. Click on "Title List" to see a master list of all the reference works that are included, such as Encyclopedia of Disability, Encyclopedia of Homelessness, Encyclopedia of Sex and Gender, and many others.
CQ Researcher an easy to use source for in-depth, analytical reporting on the most current and controversial issues of the day. Focusing on one topic, each weekly CQ Researcher provides extensive background information and discussion of various perspectives on the issue. (Use the "Quick Search" box near the top, or browse by topic if you aren't sure yet where your intrests lie.)
For tracking down a specific policy or law or the background ( legislative history) of the law. There are several good choices for this depending on where you are starting and what you are trying to find.