The Veterans Affairs (VA) PHarmacogenomic Testing for Veterans (PHASER) program, started in 2019, involves implementation of pharmacogenomic (PGx) screening so that patients and providers have access at the point of care to PGx test results of ten genes that affect prescribing of 37 common medications. The goal of PHASER is to offer 250,000 Veterans PGx testing in order to improve efficacy and reduce toxicity and costs related to pharmacotherapy. PHASER intends to reach 45-50 diverse VHA health care facilities by the end of 2023. Realizing the health benefits of PGx testing requires uptake by various stakeholders within a health care system, including patients, providers, and administrators. The objective of this partnered evaluation is to accelerate use of PGx testing in the VA. The goal of this project is to identify implementation determinants, strategies, and outcomes that affect adoption, and effects on patient medication adherence. In Aim 1, we will conduct interviews of key stakeholders at participating facilities, guided by the Consolidated Framework for Implementation Research to specify organizational determinants and the Expert Recommendations for Implementing Change typology to identify implementation strategies. In Aim 2, we will interview providers at low- and high-adopting sites and use regression to identify factors associated with provider adoption. In Aim 3, we will interview patients who have and have not had PGx testing, use regression to identify factors associated with patient adoption, and survey patients who have had testing about patient-provider discussions and missed doses. Finally, we will assess costs of implementing the PGx testing from the VA perspective. Data sources include qualitative interviews of administrators, providers, and patients; PHASER program data managed by the VA Informatics and Computing Infrastructure; and a patient survey. The PHASER program addresses VA Strategic Analytics for Improvement and Learning quality measures and Centers for Medicaid and Medicare Meaningful Measures. The immediate effect of this evaluation will be to provide the PHASER program with actionable information to optimize implementation processes. This groundwork will create a blueprint to facilitate implementation of future genomic medicine interventions and initiatives across the VA.