The principles of operation, performance issues, application guide, market status and power system studies required for high power variable speed drive systems is presented in this tutorial. The focus of the tutorial is on the Line Commutated Inverter (LCI) and Voltage Source Inverter (VSI) drives. The tutorial spans from entry level topics such as a survey of high power, power semiconductor devices, to intermediate level topics including drive configuration, high dv/dt stresses applied to VSI drives and drive control techniques, to in depth analysis of advanced topics including the factors influencing inter-harmonic levels in variable speed drives, and torsional vibration of the variable speed drives by harmonics and inter-harmonics. Several practical examples obtained from simulation studies carried out on power systems comprising variable speed drives are presented which discuss these issues. A comprehensive performance comparison of all practical drive configurations and power semiconductor devices is provided. The advantages and disadvantages of each configuration for different market sectors are highlighted.