Community-engaged research (CEnR) is experiencing a resurgence as a way of informing community-level change and policymaking. Yet the rules and regulations that are crucial to policy implementation and success are relatively understudied through CEnR. This case study of CEnR on a Medicaid service definition for tenancy supports illustrates the benefits of engaging a policy advocate in regulatory research. These include the advocate’s relationships with stakeholders; her knowledge of the regulatory domain, process, and context; and her visibility as a team member. The case also illustrates challenges to advocate–researcher collaboration, including time demands, differing goals, risks to advocate relationships, and the politicized nature of advocacy. The case depicts strategies that address these challenges, including advocate compensation time, early engagement, discussions of motivations and expectations, and proactive attention to the advocate’s role.