Social workers provide more social services to populations across the life span than any other human service profession, including psychiatry, nursing, and psychology. The scientific methodologies and the scientific knowledge relevant to social services have expanded dramatically in the last 30 years. Using the two indicators of the total number of journals and the impact factors of those journals, it would appear that social work's contribution to that expanding scientific knowledge base has been relatively limited. The purpose of this article is to examine the relationship between social work and science and to propose the outlines of a science of social work that intends to serve as a catalyst for shaping social work into a scientific discipline. (Contains 2 figures.)