SALSA Titolo: Harnack principles and free boundary problems. Abstract: After the seminal works of Luis Caffarelli in the eighties, Harnack principles of various type have played a relevant role in theory of free boundary problems governed by elliptic and parabolic problems. In this talk we present some of the most recent results on the regularity of two phase problems with right hand side, based on a new approach due to Daniela De Silva.