The Cahn–Ingold–Prelog priority rules, CIP system or CIP conventions (after the scientists;Robert Sidney Cahn, Christopher Kelk Ingold and Vladimir Prelog) are a set of rules used in organic chemistry to name the stereoisomers of a molecule. A molecule may contain any number of stereocenters and any number of double bonds, and each gives rise to two possible configurations. The purpose of the CIP system is to assign an R or S descriptor to each stereocenter and an E or Z descriptor to each double bond so that the configuration of the entire molecule can be specified uniquely by including the descriptors in its systematic name.