Conopeptides are a large family of peptide toxins produced by marine cone snails. They act with high potency and exquisite specificity on a range of ion channels and transporters of the nervous system, making them valuable drug leads and important molecular probes in neurophysiological studies. Most conopeptides are small, ranging from 10 to 30 amino acid residues, but some contain up to about 90 amino acids. They display a large chemical diversity because they have very diverse sequences and a large number of post-translational modifications. Disulfide-rich conopeptides are commonly referred to as conotoxins, and have particularly diverse structures and a broad range of molecular targets. One conotoxin, MVIIA (also named Prialt® or ziconotide), is an N-type calcium channel blocker that is used clinically as an analgesic to treat neuropathic pain. Other conopeptides have also attracted considerable interest for their potential pharmaceutical applications. In this chapter, the marine cone snails and their venoms are introduced and the chemical diversity of conopeptides is described, along with the techniques used to unravel this diversity. The three-dimensional structures of conopeptides are discussed and linked to their pharmacological activities.