Most comparative studies of the physiological and pharmacological properties of the receptors and ionic channels of various animal species have so far stressed the differences. More recent studies based on the knowledge of the primary structure of these proteins as obtained using molecular cloning techniques emphasize the common features and have led to the concept of superfamilies. These superfamilies are believed to be derived from common ancestors through evolution. To understand how this happended, it is necessary to compare the sequences and the properties of the receptors in species suffficiently distant in the evolutionary tree. In this work, specialists in the field of comparative molecular neurobiology, most of them working on both vertebrate and invertebrate species, report their recent findings concerning the three most important superfamilies: the Ligand-Gated Ion Channels superfamily (n-ACh, GABA, Glycine), the Second-Messenger Linked receptor superfamily (m-ACh, catecholamines, peptides) and the Voltage-Gated Ion Channels (Na+, K+ and Ca2+) superfamily.