This literature review examines the models, theories, and research in mathematics education that are informed by Lee S. Shulman's construct, Pedagogical Content Knowledge. The application of the concept differs in nature and volume across levels of schooling. The research includes substantial work at the elementary level, fewer studies at the secondary level, and a limited but increasing number at the university level where future teachers are prepared. Even with the differences in volume across grade bands, a significant use of PCK is evident in the literature on mathematics education.