Among the several distinct ways of formulating and quantizing a Hamiltonian system, the light cone approach enjoys a special status because it has the largest stability group. The aim of this volume is to present achievements and open problems in this rather unusual quantization framework to a large audience. The formulation is set up in the introduction where the issues are also indicated with specific examples: vacuum structure, signature of non-perturbative effects, chiral symmetry breaking, light cone gauge theories, and more. The chapters that follow address these topics through a selection of the most relevant contributions presented at Les Houches.