Ion implantation is finding increased usage in device fabrication owing to precise control and reproducibility of the charge and depth distribution of the implanted-dopant profile. The MOST illustrates the application of charge control through threshold-voltage adjustment and though predepostion for drive-in diffusion to form complementary devices. A compilation of range-energy data for B, P, and As in silicon is given along with factors which influence the implanted-dopant distributions after anneal treatments. Implantation procedures are presented for high-frequency bipolar transistors which depend critically on both charge and depth control of the emitter and base profiles. Another important aspect of ion implantation is lateral control, a feature which is necessary for high packing density circuits. Disorder effects associated with implantation through oxide masks are discussed. A brief account of implantation for GaAs devices is also included.