Social Work Almanac, 2nd ed (book) by 
Statistical Handbook on the Social Safety Net (book) by 
Statistical Handbook on the World's Children by 
A Dictionary of Social Work and Social Care, 2nd ed (E-book) by 
The Encyclopedia of Social Work (E-book) by 
Social Policy: Essential Primary Sources (E-book) by 
Social Workers' Desk Reference,3rd ed (E-book) by Subject encyclopedias provide a concise overview of your topic, often including history, current state, policy issues and relevant theories, while specialized dictionaries provide definitions of terms or phrases unique to the field.
Encyclopedia of Social Welfare History in North America (book & e-book) by 
Handbook of Military Social Work (Book) by 
Comprehensive Handbook of Social Work and Social Welfare, the Profession of Social Work (book) by 
The Oxford Handbook of Social Work in Health and Aging by