Summary: “Learning” is a complex phenomenon that is studied in different scientific disciplines. A computer program with the ability to “learn” contains mechanisms for gathering and evaluating information and, consequently, for improving its performance. Algorithmic Learning Theory provides a mathematical foundation for the study of learning programs. It is concerned with the design and analysis of learning algorithms. The analysis proceeds in a formal model such as to provide measures for the performance of a learning algorithm or for the inherent hardness of a given learning problem.