Based on the formal concept of knowledge structures originally proposed by Jean Claude Falmagne and Jeal-Paul Doignon, methodological developments and experimental investigations as well as applications are described for various knowledge domains. This monograph includes three main topics: theoretical issues and extensions of Doignon and Falmagne's theory of knowledge structures; empirical validations of specific problem types and knowledge domains, such as sentence comprehension, problem solving in chess, inductive reasoning, elementary mathematical reasoning and others; and application of...