Ion assisted deposition of optical coatings has been studied for many years at a fundamental level. Progress in ion source technology and process control has led to industrial applications and to the introduction of ion- and plasma-assisted coating technologies into the production of optical components. Ion- or plasma-assistance leads to characteristic changes in film structure, which induce special properties in the coatings. A particular advantage is the deposition of durable coatings without the addition of thermal energy. This opens a number of applications of optical coatings on temperature-sensitive substrates. The paper gives an overview over the developments of ion-assisted deposition (IAD) coating technology, and summarizes the possible benefits as well as drawbacks that are associated with ion- or plasma-assisted deposition of dielectric optical coatings.