This thesis explores the knowledge transfer between academia, industry and the national innovation system through the mobility of PhD graduates and other knowledge transfer mechanisms. The first chapter explores how PhD graduate mobility gives a different image than patents, as well as the impact of having a PhD aligned with the industrial specialization of the country on the likelihood of knowledge transfer toward the regional innovation system. The second chapter explores how different factors impact the attraction of prospective PhD students and their retention after graduation. Finally, the third chapter explores a case of a knowledge relationship between a university and one of its spin-offs and their knowledge exchange over time.