Overview and Context for Spacecraft Momentum Control -- Agile Spacecraft Dynamics and Control -- Requirements Development for Momentum-Control Systems -- Dynamics of Momentum-Control Devices -- Inner-Loop Control of Momentum-Control Devices -- CMG Arrays -- CMG Singularities -- Steering Algorithms -- Motors in Space -- Bearings and Lubrication in Space -- Integration and Test -- Commercial and Academic Flight Heritage of CMG -- Current State of the Art.