The paper examines ways of teaching the physical concept of wave fronts in two dimensional waves. The concepts that examined are: Wave fronts, rays, refraction, determination of the refracted wave fronts with two methods, propagation of waves in a medium where the wave velocity changes gradually.. In the last part is examined the application of the concept of wave fronts in lenses and Huygens' method of finding the shape of a ‘perfect; lens. The students' difficulties with connection with all these subjects are presented.