In order to maneuver satellites accurately from one attitude to another, onboard rate sensing gyroscopes usually must be calibrated after launch. Several algorithms have been used to determine gyro biases, misalignments, and scale factors. This paper describes algorithms that have been used in the past, discusses their advantages and limitations, and describes a new algorithm and the gyro calibration results obtained using this new algorithm. The new algorithm has significant operational advantages in addition to being at least as accurate as other algorithms.