Three-dimensional geologic interpretation of surface and subsurface data requires integration and application of both geologic knowledge and spatial cognitive skills. Much surface geologic mapping still employs pen and paper techniques, but subsurface interpretation is usually accomplished using sophisticated visualization software. In both cases, successful interpreters use mental models that bridge internal and external forms of 3-D visualization to construct 3-D geologic interpretations. This AAPG Memoir 111 sets out to understand more about the convergence of geology, 3-D thinking, and software, which collectively provide the basis for truly effective interpretation strategies. It should appeal to all geologic interpreters, and especially those who investigate and teach interpretation skills.