In organic chemistry, a directing group (DG) is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent.  The term is usually applied to C–H activation of hydrocarbons, where it is defined as a "coordinating moiety (an internal ligand), which directs a metal catalyst into the proximity of a certain C–H bond." In a well known example, the ketone group () in acetophenone is the DG in the Murai reaction.
The Murai reaction is related to directed ortho metalation, a reaction is typically applied to the lithiation of substituted aromatic rings.
A wide variety of functional groups can serve as directing groups.