The Burst and Transient Source Experiment (BATSE) is a highly sensitive, all‐sky monitor for the Gamma‐Ray Observatory (GRO). The eight scintillation detector modules of BATSE are positioned around the GRO spacecraft provide a uniform view of the entire sky above the horizon. Each module is 20 in. in diameter, 0.5 in. thick and operates in the energy range from 40 to 600 keV. Rough burst locations can be derived from the relative counting rates of the detectors; longer‐lived (≳100 min) transient sources can be detected and located by Earth occulations. The data system contains mass memory to allow storage of large amounts of burst data in short time intervals. Data are sorted onboard in various ways into programmable energy, time and detector domains. Details of the design and capabilities of the BATSE are presented.