The unit commitment problem is a fundamental problem in the electric power industry. It addresses a fundamental decision that is taken when operating a power system, namely to set the schedule of power production for each generating unit in the system so that the demand for electricity is met at minimum cost. The schedule must also ensure that each unit operates within its technical limits; these typically include ramping constraints and minimum uptime/downtime constraints. Units that are scheduled to produce electricity during a given time period are said to be committed for that period. Unit Commitment in Electric Energy Systems presents the most relevant mathematical optimization models for the unit commitment problem. It is an ideal starting reference for practitioner and researchers interested in this important and challenging problem, as it introduces the key technical details and summarizes their significance.