A series of computer-generated films is described, intended to serve as pedagogic aids in presenting ideas concerning the motion of electrons in periodic potentials. Three films have been produced which illustrate the following phenomena: (A) propagation of wave packets of several different mean energies through the ideal crystal lattice; (B) reflection and transmission of a wave packet incident on a crystal from free space, for mean energy values lying (1) in an allowed energy band of the crystal and (2) in a forbidden gap of the crystal; and (C) scattering of a wave packet by an impurity atom in the lattice.