This chapter covers the computation of synthetic seismograms, or theoretical seismograms. This involves predicting, via computation, what seismic traces might look like for a given subsurface medium model. The relatively simple case of vertically traveling waves in a sequence of flat horizontal layers is discussed in relative detail, including how to compute wave amplitude losses due to reflection, transmission, geometrical spreading of wavefronts, and absorption. The generally more complicated case of nonvertically traveling waves is also briefly summarized. More complete methods such as the finite difference and finite element methods are briefly mentioned. Also covered are the reflectivity function and the interference effects that occur for waves with nearly equal arrival times, such as the tuning effect. The chapter ends with an appendix showing examples of synthetic seismograms computed with the finite difference method.