A digitally programmable microwave source, assembled from various commercially available components and covering the range 8.0–40.0 GHz in four bands, has been interfaced to a small computer, and software has been developed for the acquisition, storage, retrieval, and statistical analysis of data. This system has been used in conjunction with Stark and Zeeman modulated microwave spectrometers, yielding high resolution, high sensitivity, high accuracy, and operation with a considerable degree of automation and flexibility. The programming time is typically 5–15 msec, and the frequency may be set in increments of 100 Hz or less. The long term frequency stability and accuracy is 2×10−9/month, and the short term stability or spectral purity appears to be excellent, in agreement with theoretical expectations. The software provides for signal averaging, baseline subtraction, convenient display and frequency measurement, and for transfer of data, via magnetic tape, to a large scale computer, where it can be analyzed by a nonlinear least squares procedure.