Galactic globular clusters have always been at the crossroad of several investigations in both Stellar and Galactic Astrophysics. For long time, they have been considered the prototypes of Simple Stellar Populations, and hence used for testing and calibrating stellar evolutionary models as well as population synthesis tools. Nowadays, after the discovery of the presence of multiple stellar populations in almost all Galactic GCs, we know that this assumption is no longer valid. The process(es) of formation and early evolution of these star clusters is (are) very far to be understood, and any scenario so far envisaged is severely challenged by the pletora of empirical evidence collected till now. In the same time, thanks to the availability of an impressive observational framework - collected by combining kinematic measurements from Gaia mission, with data provided by large spectroscopic and photometric surveys -, GCs are playing a crucial role for our understanding of the assembly history of the Milky Way. We will review our present knowledge about these important stellar systems, discussing the several, open issues related to their formation/evolution, and discuss how we can use them in our effort to depict the Milky Way assembly history.