Self-replicating molecules stand at the very boundary of chemistry with biology. This review describes the development of synthetic structures capable of self-replication from studies in molecular recognition. The weak intermolecular forces--hydrogen bonds and aromatic stacking interactions--that characterize interactions of nucleic acid components were designed into synthetic receptors for adenine. Covalent conjugates of these receptors with adenines gave self-complementary structures capable of replication. The new systems feature autocatalysis, sigmoidal product growth and even mutation. General rules for the design of replicating systems are described and these suggest that the evolution of replicating molecules was an inevitable event.