This paper is in part a review but it also contains some original work. It deals with the manner in which shock waves are formed from finite compressions in gases and describes something of the structure of the shock front itself. The principal features of the behavior of shocks in reflection, refraction, and diffraction are discussed with particular attention given to anomalous observations and comparison with simple theories. Some results are given for shocks in real molecular gases showing relaxation effects. Quite a number of illustrations are included from the authors' own observations in the shock tube. The treatment is not exhaustive but covers many points likely to be of interest to teachers of physics.