Despite endemic problems in the family support field, the subjects of engagement and retention in voluntary services have not received the sustained focus of theorists. Few have specified and systematically tested the causal mechanisms that explain why parents fail to participate voluntarily in therapeutic or supportive services. Most studies that have addressed this question have operated within a very restricted conceptual framework, often limiting their models to specific participant and program characteristics. The purpose of this four-year effort has been to develop and test an integrated theory of parent participation that reflects the interrelationship and interdependency of individual, staff, and program attributes. The study drew its participant and program samples from a major family support initiative known as Healthy Families America (HFA) which has over 400 sites across the country. Two samples were utilized in the research – a retrospective sample of 815 participants served by one of seventeen HFA programs, and a prospective sample of 343 new parents served by nine HFA programs. To capture the unique influence of these various factors, the study employed hierarchical linear modeling (HLM) to refine an understanding of what factors increase the use of voluntary support services. HLM is a statistical procedure that is designed to investigate relationships between variables that are measured at different levels in a hierarchical or nested structure. Specifically, HLM and other related techniques allow us to determine the extent to which individual, program, and community factors influence service utilization decisions.