Best practices for the design, delivery and evaluation of harm reduction programming include the meaningful and equitable engagement of people who use drugs. This means engaging people who use drugs (including current and past use) in all aspects of harm reduction programing, including design, implementation, delivery and evaluation. People with lived experience have the knowledge and skills required to play a central role in harm reduction programming. This article summarizes available literature and discusses the importance of the meaningful engagement of people who use drugs, sometimes — and controversially — called “peers,” in harm reduction programs. This includes information on the roles that people who use drugs take on in programming, the advantages of their engagement, and barriers and facilitators to their engagement.