Plasma power supplies display a marked interaction with the plasma and other elements of the system, and a clear understanding of the important parameters and characteristics of the power supply is a considerable aid in designing and operating a plasma system. In this presentation the basic characteristics of DC, midfrequency, and high frequency (RF) supplies will be outlined, and the key parameters vis-à-vis plasma interactions presented. Instrumentation and matching issues in RF systems will be discussed; in particular a presentation will be made on forward, reflected and load power and their significance in plasma systems. Finally, special and emerging power technology will be covered in a special section, including balancing systems for dual magnetron sputtering, multiple anode sputtering, and ultrahigh power pulsed DC, among others.