This lecture delves into the global infrastructure investment gap, estimated at one trillion US dollars annually, discussing the reasons behind it, such as aging infrastructure in developed countries and growing needs in developing countries. It explores how public-private partnerships (PPPs) can help address this challenge by saving costs, transferring risks, introducing innovation, and speeding up project delivery. The lecture also highlights the challenges faced by both governments and the private sector in implementing PPPs, as well as the disadvantages and potential future developments of PPPs in the context of closing the infrastructure gap.