The expansion of human immunodeficiency virus (HIV) care and treatment in Africa and other resource-limited settings has begun to mitigate the impact of the acquired immunodeficiency syndrome pandemic. As this expansion has occurred, critical research has been conducted that has helped to define best practices and establish guidelines in HIV care. However, despite this research, a tremendous gap exists between the actual delivery of care and those strategies with proven efficacy in the clinical research setting: the program-implementation gap. The field of implementation research has the potential to fill this knowledge gap and to address the barriers to the effective replication of evidence-based interventions in local settings. This article reviews the current understanding of the field of implementation research and discusses its association with other areas of health services research, clinical research, and quality management work. Opportunities for conducting implementation research are proposed, and future steps to develop the field are outlined.