This primer proposes a new definition for public-private partnerships (PPPs) in health that opens up a flexible range of partnering opportunities while emphasizing the importance of formal agreements and honest brokers in the process. The primer differentiates three types of PPP engagement, using real world examples to illustrate communication, cooperation, and collaboration between actors in different sectors. The author also discusses how combining social and commercial investment will change the nature of PPPs and provides an inventory of common health system gaps that they can address.