This article includes a description of a family-systems model for implementing early childhood and family support assessment and intervention practices. The model includes both conceptual and operational principles that link theory, research, and practice. Lessons learned from more than 20 years of research and practice have been used to revise and update the model, which now includes a major focus on family capacity building as a mediator of the benefits of intervention. Key components of the most recent version of the model are described, and findings from research syntheses showing the relationship between the different components of the family-systems model and parent, family, and child behavior and functioning are summarized. Future directions are described. (Contains 3 figures and 3 tables.)