A method has been developed allowing the direct inversion of seismograms to obtain an estimate of the seismic source, as characterized by its equivalent force moment tensor. With reasonable assumptions the problem can be shown to be linear in both the frequency and time domains and least-squares methods are used to estimate the source mechanism. In the synthetic tests that have been run, several possible uses of the method have been investigated. With a satisfactory station distribution the source mechanism can be recovered using complete seismograms from three component stations or several P arrivals on vertical components. The method is useful in distinguishing multiple events including explosions. The errors of the fits are determined in the procedure and yield information such as the bandwidth of useful data in the frequency domain and error estimates for fault-plane solutions in the time domain fits.