Atomic layer deposition offers unique advantages compared to more classical PVD coating processes. These advantages include an inherently high coating thickness homogeneity and conformal coating of both micro-optical structures, such as gratings, and large free-form optics, such as aspheric lenses. The talk will introduce the coating process, compare its properties to those of more classical PVD processes and give an overview of recent developments of ALD coatings in optical applications.