The behavior of the head wave from a high-speed layer embedded in a low-speed half-space has been investigated with 2-dimensional seismic models. Twelve layer thicknesses ranging from 4 wavelengths to one-tenth wavelength were used. A simple theory based on interference between the head wave and the reflections from the bottom of the layer gave amplitude-distance values which agreed with the observations for layer thicknesses down to about one-third of a wavelength. For thick layers, the experimental amplitude dependence on distance was different from the theoretical law (- 3/2 power of the distance). The velocity minimum for thin layers discovered by Lavergne was confirmed and a possible slight velocity maximum at intermediate layer thicknesses noted. The velocity for zero layer thickness appeared to be greater than the free bar velocity. Systematic variations of head-wave spectra with layer thickness occurred.