This lecture explores the efficiency and mechanisms of ATP Synthase, focusing on the F-type and V-type ATPases. It covers the model for ATP Synthase, the efficiency of the engine, Brownian motion for protons, energy production from ATP hydrolysis, and the role of ATP Synthase in various organisms. The lecture also delves into the structure and conformational states of mitochondrial ATP synthase, as well as the proposed role of V-ATPases in membrane fusion.