Background sources provide overviews of a topic, definitions of terms, biographical sketches of key persons, important theories, statistics, and recommendations for further reading. Background information from special encyclopedias, dictionaries and handbooks can be very useful in providing a focus and guidance for research.
Blackwell Handbook of Social Psychology
Diagnostic and Statistical Manual of Mental Disorders - DSM-5
Encyclopedia of Group Processes and Intergroup Relations
The Encyclopedia of Social Work
The Oxford Handbook of Social Work in Health and Aging
Social Workers' Desk Reference
The Blackwell Companion to Social Work
Dictionary of Social Work
Encyclopedia of Aging by 
The Social Workers' Toolbox
Social Work Fields of Practice