This book constitutes the refereed proceedings of the 23rd International Conference on Algorithmic Learning Theory, ALT 2012, held in Lyon, France, in October 2012. The conference was co-located and held in parallel with the 15th International Conference on Discovery Science, DS 2012. The 23 full papers and 5 invited talks presented were carefully reviewed and selected from 47 submissions. The papers are organized in topical sections on inductive inference, teaching and PAC learning, statistical learning theory and classification, relations between models and data, bandit problems, online prediction of individual sequences, and other models of online learning.

The "Stats in the Chateau" summer school was held at the CRC chateau on the campus of HEC Paris, Jouy-en-Josas, France, from August 31 to September 4, 2009. This event was organized jointly by faculty members of three French academic institutions ENSAE ParisTech, the Ecole Polytechnique ParisTech, and HEC Paris which cooperate through a scientific foundation devoted to the decision sciences.

The scientific content of the summer school was conveyed in two courses, one by Laurent Cavalier (Universite Aix-Marseille I) on "Ill-posed Inverse Problems," and one by Victor Chernozhukov (Massachusetts Institute of Technology) on "High-dimensional Estimation with Applications to Economics." Ten invited researchers also presented either reviews of the state of the art in the field or of applications, or original research contributions.

This volume contains the lecture notes of the two courses. Original research articles and a survey complement these lecture notes. Applications to economics are discussed in various contributions.