Communities are integral parts of health systems and their engagement in defining health needs, priorities, solutions and in the delivery of services is essential to improving health and well-being. All communities, regardless of how they are defined, include individuals or sub-groups who, for a host of reasons are disadvantaged and experience a disproportionate burden of ill health. Identifying and engaging them is both essential and challenging, and should be prioritized. Communities interface with the health system with varying degrees of engagement ranging from passively receiving information at one end of the spectrum to actively engaging in decision making through mutually accountable relationships at the other. This chapter explores the concepts of community and community engagement and consider their role in health systems. It examines the concept of health, the changing health needs of communities and the influence of community in defining health issues and informing solutions, including the delivery of services. Finally, the chapter discusses the modalities of community engagement for health systems, particularly within low- and middle-income countries (L&MICs).