A wide variety of energetically assisted methods have been employed to grow diamond films at low pressures. Common features of the processes include the presence of atomic hydrogen, energetic carbon containing fragments and high surface mobilities. Some understanding of the molecular processes taking place during nucleation and growth of diamond has been achieved, but detailed molecular mechanisms are not known with certainty. Application of vapor grown diamond for abrasive grit, tool coatings and wear resistant surfaces can be expected shortly. However, the use of vapor grown, crystalline diamond in optical applications or as active semiconductor elements will require further control over surface roughness and crystalline quality. Related research has led to the discovery of a new class of materials, the so-called "diamondlike" phases. Two types of diamondlike materials may be distinguished, namely, the diamondlike hydrocarbons and the diamondlike carbons. These materials possess exceptional hardness, smoothness and chemical inertness. They show promise as combined anti-reflection and abrasion resistant coatings on optical elements, as protective coatings on magnetic and optical disks, as diffusion barriers and for photo-lithographic applications.