Microstructure is critical for polycrystalline thin film applications and its control during kinetically-limited, low-temperature deposition has been an important goal of materials science in the past decades. In this part of the workshop we will review the fundamental film growth processes - nucleation, coalescence, competitive growth, and recrystallization - and their role in thin film microstructure evolution as a function of substrate temperature. We discuss, further, atomistic mechanisms through which reactive deposition and low-energy ion/surface interactions modify growth kinetics and, thus, allow to controllably manipulate microstructural evolution. Special attention will paid to in-situ substrate treatment by ion-irradiation and its effect on film microstructure and adhesion.