This article first defines inertial navigation and then considers a typical accelerometer. The basic law of gyroscopics is then derived, and the distinction between free, rate, and integrating gyroscopes is made. The design of the components of a gyro is discussed; ball and gas bearings for gyro wheels, gimbal suspensions (both floated and unfloated), and types of pickoff and torquer are mentioned, also a component which combines both in one unit. Future types of gyroscope are discussed, among them the electrostatic, cryogenic, laser and nuclear spin gyroscopes.