This review focuses upon major achievements and recent advancements in the development of photoactive molecules which, under controlled illumination, release acidic groups either in solution or at the solid state. Successful photoacid generators are described the design of which are based on ionic, benzyl ester, imino ester, spiropyran and terarylene frameworks and the mechanism of acid generation in each case is discussed in detail. The development of such systems towards applications in lithography, surface etching, polymer design and two photon absorption processes are presented in order to give a state of the art overview of the development of new photoacid generators in the last three decades.