We present a detailed study of the characteristics of electro-optic sampling of ultrashort terahertz (THz) pulses including frequency-dependent phase matching, reflection, dispersive propagation, and absorption. In particular, we investigated the origin of the oscillatory tail that is often observed in electro-optic sampling traces and found that this tail results from the dispersive propagation of the THz pulse through the electro-optic crystal. For extremely broadband THz pulses, the THz pulse is additionally distorted by reflection and absorption in both the generation and the electro-optic detection crystal. The modeling of the distorted electro-optic sampling trace permits a detailed reconstruction of the initial THz pulse.