The effective design of stable, ordered organic superlattices is assisted by a thorough understanding of enthalpy and entropy contributions and molecular interactions in two dimensions. Important information in this respect can be obtained by studying the thermal stability of monolayers of long-chain organic amphiphiles. Work on both LB and SA films is reviewed and a possible explanation for thermally-induced structural events (e.g. order-disorder transitions, see figure) in molecular assemblies discussed.