Electrical plants on-board modern cruise ships, offshore rigs and other naval vessels have nowadays reached a size and complexity comparable or even superior to big industrial plants and power plants. The continuous increase of the size of ships and the widely accepted adoption of electrical propulsion has led to the installation of HV (MV) power generation and distribution plants of very high power, tens of MW. Everybody who plans, manages or services these complex on-board power plants nowadays must have knowledge as well of HV plants and electrical machines, power converters, protection relays, of control and automation systems. This book intends to be an overview of technical features and planning issues of these electrical plants. It is meant to bear general validity, even if it is focused on larger ships with HV plants and electrical propulsion.