The feasibility of building a two-cell cesium gradient magnetometer with a sensitivity of 0.1 mgamma has been demonstrated. The theory of operation of an optically pumped magnetometer has been used to determine the cell performance required to obtain a sensitivity of 0.1 mgamma. A cell development program has resulted in buffered cesium cells which exhibited signal-to-noise ratios of 100 dB 1 Hz and traverse relaxation times of about 7 ms. Unbuffered cells with signal-to-noise ratios of 85 dB and relaxation times of about 13 ms were also made. These cell performances are near, or above the theoretical requirements. Tests of a single sensor magnetometer showed a sensitivity of 1 mgamma for a 90 Hz magnetic field.