Introduction to the Yang-Mills quantum theory

A pedagogical discussion of the Yang-Mills quantum theory is presented. A somewhat unconventional description makes use of physical, quantum-mechanical ideas, rather than of formal, mathematical developments. The purpose is to highlight those aspects of the model which have been exposed in the last few years by semiclassical methods, but without using semiclassical approximations. This requires a careful treatment of the non-Abelian gauge symmetry present in the theory.