The implementation phase has been less studied until the seventies of the last century. The classic book Wildavsky and Pressman Implementation (1973 ) resulted in ever deeper studies on the interplay between initially decided and the implementation of public policies. Implementation and evaluation are two sides of the same coin. We are referring to the study of the interaction between public policy objectives and actions taken to achieve them. We will study the different models of implementation of public policies and we emphasize the importance of the actors in this process.