In this article, the effect of thermal expansion on laminated composite plates are examined and the influence of the layup is studied using non-dimensional lamination parameters. A maximum of 12 parameters are needed to describe all possible laminates regardless of the number of plies. In some applications, the layup is selected to minimum thermal expansion in a certain direction. We show that thermal expansion cannot be prevented in all directions. Thermal deflections of symmetrically laminated plates that are continuous over many line supports are determined using the Rayleigh-Ritz method. The constitutive equations and the thermal loads are expressed in terms of four non-dimensional lamination parameters. Layups that minimize thermal deflections are determined for several types of composite plates subjected to temperature increases that vary linearly through the thickness.