Abstract: The diffraction and interference of light are easily observed phenomena that five direct, tangible evidence of the wave nature of light. Diffraction is at the root of many technologies, scientific techniques, and common visual phenomena. Students explore diffraction by shining a laser at a hair, a variable-width slit made from pencils, wire meshes of various size and diffraction gratings. After an introduction to single-slit and N-slit diffraction equations, students are faced with tree challenges: to measure the track spacing in a CD and DVD, to determine the relative thickness of hairs, and to estimate the diameter of a lycopodium spore. In the last two challenges, students design their own procedure.