Reference sources are invaluable for defining key concepts, providing brief overviews of a subject, and identifying major theories and research developments. They can provide you with the background you need to select and develop a topic of research, or help you explore internship or career opportunities.
Subject encyclopedias provide an overview of your topic, often including history, current state, policy issues & relevant theories, while specialized dictionaries provide definitions of terms or phrases unique to the field.
Comprehensive Handbook of Social Work and Social Welfare, the Profession of Social Work by 
Encyclopedia of Social Welfare History in North America by 
Social Policy: Essential primary sources by Another great source for overviews of social issues:
