Policy scholars generally agree that greater coherence of policies is desirable, but the concept is under-theorized and has received little empirical examination. This research examines the policy coherence of 18 policy domains and considers institutional factors that affect variation among them. There is considerable variation in coherence among substantive, regional, and identity-based policy domains. Greater degrees of policy coherence exist for policy domains that have dominant congressional committees or have more involvement of lead federal agencies. These findings extend what policy scholars know about policy subsystems in American policymaking to consideration of the coherence of policy domains.