This paper discusses the development of appropriate private sector participation (PSP) to optimize the provision of air transport infrastructure (ATI). It is aimed primarily at government policy makers in low- and middle-income countries and their advisors. This paper answers a number of questions, including the following: When is it appropriate to allocate the responsibilities involved in ATI provision to private firms rather than continue to allocate them to governments and their agencies? If policy makers decide to vest certain responsibilities with private firms, what considerations are important during this allocation process? How is it best to achieve the transition, and what kinds of private firms should be involved?