A low‐energy electron diffraction apparatus has been built and used to study the adsorption of simple gases on platinum (100), (110), and (111) faces. Some simple structures formed on various faces are described. Adsorption of oxygen on the (110) face is shown to lead to a rearrangement of the top layer of Pt atoms. On the basis of single scattering it is shown that the adsorbate‐substrate combination leads to reflections to be expected from each lattice considered separately. When double scattering is permitted, reflections appear in positions given by the sums and differences of the reciprocal lattice vectors of the separate lattices. This double scattering or multiple reflection is shown to play an important role in low‐energy electron diffraction. In particular, two sets of complex diffraction patterns formed by oxygen on the Pt (100) face are shown to have an easy interpretation in terms of multiple reflection. The simple oxygen structures formed are rotated with respect to the Pt substrate but form coincidence lattices with it.