In the early 1970's the term "neuropeptide" was used for the first time by David de Wied for peptides related to peptide hormones but with non-endocrine biological activity in the brain. This early notion appreciated neuropeptides as a specific class of chemical signals produced by neurons, released in a regulated fashion and acting on other neural cells. As we define them today, neuropeptides are encoded by over 70 genes in mammalian genomes. Neuropeptides can be clustered in at least 10 subfamilies according to structural features, for which often shared or related receptors exist. A complete overview is provided through hyperlinks to bioinformatic databases on genome and transcripts, protein structure and brain expression. Other proteineous signaling molecules in the nervous system which originally were discovered in other biological systems, particularly chemokines, growth factors and peptide hormones, share the hallmarks of classical neuropeptides and may be considered as neuropeptides as well.