By virtue of its excellent electronic properties, diamond may become an important material for high temperature, high speed, high power and high compact electronic devices. However, most of these devices, single crystal or epitaxial films are required. Thus, for obvious reason, large-area heteroepitaxial diamond films are desired. Silicon is the most important material severed as a substrate for diamond heteroepitaxy. However, diamond can hardly be grown on mirror-polished Si, with nucleation density being only about 104 cm−2. Although scratching Si substrate could enhance greatly the nucleation density, it destroyed seriously the periodic structure of the Si surface. Thus diamond film grown on such a substrate will be randomly oriented polycrystallites. In order to overcome this difficulty, several methods have been developed, including (1) bias enhanced nucleation; (2) electron emission enhanced nucleation; (3) nucleation enhanced by slight surface modification; and (4) very low pressure ( 0.1 torr ) nucleation. We will introduce the second, third, and fourth methods, which were developed in our laboratory recently. Special attention will be paid to the relation between heteroepitaxy and high density nucleation. The incubation time for diamond nucleation is a critical parameter for high density nucleation and heteroepitaxy.