The available geodetic and teleseismic data sets for the 1923 Kanto earthquake (Ms = 8.1) have been combined into a joint inversion for both temporal and spatial slip variations. We assumed an initial faulting model to be consistent with the geometry determined by Kanamori (1971) on the basis of first-motion data, aftershock area, and the amplitude of surface waves at teleseismic distances and also to enclose the slipped area estimated by Matsu'ura et al. (1980) from the geodetic data employed here. We then inverted for a heterogeneous distribution of slip of the fault plane. The leveling routes and triangulation stations used (consisting of 225 bench marks and 31 triangulation points) are from Matsu'ura et al. (1980). We chose to first determine the overall, static slip distribution by inverting the geodetic data alone. We then proceeded to gradually increase the importance of the teleseismic data, always requiring a good fit to the geodetic leveling and horizontal displacements. In this way, we could provide a constraint on the overall static slip characteristics from the geodetic data and provide stability for the teleseismic inversion, yet determine the degree of slip heterogeneity and time history most suitable for matching the waveform data and for simulating strong ground motions. Our analysis yields a seismic moment of 7 to 8 × 1027 dyne-cm (Mw = 7.8 to 7.9) with a maximum slip of approximately 8 m. The most concentrated slip is in the shallow central and western portion of the fault. The location of the concentrated slip on the fault plane has important consequences for the amplitude, duration, and frequency content of the resulting ground motions as documented by Takeo and Kanamori (1993).