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.
The Cambridge Handbook of Age and Ageing
Diagnostic and Statistical Manual of Mental Disorders - DSM-5
The Encyclopedia of Aging
Encyclopedia of Gerontology
The Encyclopedia of Social Work
The Oxford Handbook of Social Work in Health and Aging
Social Workers' Desk Reference
Dictionary of Social Work
Encyclopedia of Ageism
Encyclopedia of Aging by 
Encyclopedia of Aging by 
The Encyclopedia of Elder Care
The Social Workers' Toolbox