Shear-wave (S-wave) technology has been investigated for about half as long as P-waves as an exploration tool, beginning in the mid-1960s with field experiments and vertical seismic profiles (VSP) to assist interpretation. Although it was immediately recognized that the relative quality of S-wave data was unpredictable, early processing and analysis did not consider the effects of birefringence or splitting. This unpredictable behavior, along with dynamic mis-ties, observed at intersections of 2D lines, was shown in the 1980s to be a result of S-wave splitting in azimuthally anisotropic media. In addition, 20 years of the early effort were devoted to developing S-wave sources. However, ironically, it turned out that conventional P-wave sources were best; P-waves convert to S-wave (PS-wave) reflections at layer interfaces with nearly the same strength as P-wave reflections.