The Earth's magnetic field can provide attitude reference for satellites. Because of the nature of the terrestrial magnetic field, magnetic sensing is primarily used to sense azimuth, with a horizon sensor providing reference in the other two axes. The magnetometer azimuth sensor is small, light, and inexpensive. A new solid-state magnetometer based on magnetoresistive techniques can provide azimuth determination with an accuracy equal to existing techniques. It has even more favorable advantages, however, in size, weight, power consumption, and cost compared to conventional techniques. A magnetic azimuth sensing system based on this magnetometer should provide azimuth information to about 0.5 degrees, a limit imposed by uncertainties in the Earth's field rather than limitation in sensitivity of the solid-state sensor.