Abstract: We propose to study the impact of integrating behavioral health (BH) care into primary care practices (e.g., co-location of behavioral health specialists and implementation of patient care teams) on access to behavioral and mental health (MH) services, treatment, appropriate patient evaluation, avoidable hospitalizations, and quality. To accomplish this, we will study the effectiveness of the largest primary care payment and delivery reform model ever tested in the United States, the Comprehensive Primary Care Plus (CPC+) demonstration, in the context of the COVID-19 pandemic which has greatly impacted population mental health. We are uniquely positioned to examine these impacts through an established partnership with a private health insurer that covers over 2 million beneficiaries. Specifically, we will (1) categorize primary care practices along the spectrum of BH integration ranging from coordination to co-location to full integration, (2) empirically develop a new approach to categorize practices into different levels of BH integration; and (3) examine the impact of different levels of BH integration in the primary care setting on patient-level outcomes (access, BH and MH evaluation, and quality). We will combine data provided by the health insurer (medical, laboratory, pharmacy, patient, and physician) with data collected from primary care practices on which BH integration components they have implemented. Through this work, we will better understand whether and how BH integration in the primary care setting has met the increasing demand for MH and BH services caused by the ongoing COVID-19 pandemic.