AbstractThe properties of thin films are functions of film structure and hence of production route. The structure of thin films consists of macro- and microscale features such as grains, together with pits, cracks, and inclusions, all of which are characterised by their spatial distribution, size, and shape. Some basic definitions and methods that can be used to characterise quantitatively the microstructures of thin films are presented. Examples are given for TiN films produced by plasma assisted chemical vapour deposition and physical vapour deposition.