The engineering versatility of molecular organic materials, together with their attractive electronic, magnetic, and optical properties, have triggered their preparation as thin films in the last years. Although the interactions between molecules and inorganic substrates are rather weak (van der Waals, hydrogen bonding, etc.), the crystallographic phase, the type and degree of orientation, and the morphology of the resulting films critically depend on the interface and the kinetics of growth. The control of the structure and morphology of the films is thus essential when envisioning practical applications. The relevance of interfaces in the growth and doping of films is discussed, and the phenomenology of polymorphism is explored. Additional issues such as the mechanical properties are also addressed. The figure, showing a scanning tunneling microscopy image of a monolayer of bis(ethylenedithio)-tetrathiafulvalene on a Au(111) substrate, illustrates the interface issue.