The integration of behavioral health services into primary care in a rapidly evolving innovation that has shown potential to improve access to care, health outcomes, and lower health costs. In an effort to reform healthcare system, integrating behavioral health services become a vital part of the patient-centered medical home (PCMH). As research and developments in integration continue to evolve, there is a need to identify consistencies, discrepancies, and gaps in the field to inform the best ways to move forward. This study is a systematic review seeking to identify trends, gaps, and future directions of research in integrated behavioral health in primary care. Using Google Scholar 171 papers were included, 95 being original research and 76 being reviews, commentary, and editorials. From the results, it is clear that the case for integration has been made, and now it is time to move to the specifics. Both empirical and theoretical evidence supports the benefits of integration to patients and health systems. However, there is a lack of literature that tackles problems that hinder or facilitate integration in independent clinics with unique characteristics. Most notably, specific interventions that are effective and appropriate in primary care, payment reforms that are feasible and sustainable, and the effect of integration on health disparities.