Research on variation in policy implementation has examined how individual- and organizational-level variables shape discretionary practices at the frontlines of implementation but has given less attention to the influence of the organizational field. From an institutional logics perspective, the practices of street-level workers are likely to be more congruent with policy intent when policy is consistent with the core institutional logic that structures the organizational field. Using data from a probability sample of 90 Los Angeles County HIV/AIDS health organizations and 216 frontline practitioners, our findings suggest that the extent to which implementation of HIV test counseling follows guidelines of the Centers for Disease Control and Prevention (CDC) is related to consistency between CDC policy and core institutional logic, when accounting for individual-level factors such as client need; practitioners’ professional orientation, knowledge, experience, and training; and organizational constraints such as workload pressures and formalization.