To be published as a chapter in COMETS II (Ed. M. Festou) 2003. For preprint information please contact the first author. 
The current understanding of cometary rotation is reviewed from both theoretical and observational perspectives. Rigid body dynamics for principal axis and non principal axis rotators are described in terms of an observer's point of view. Mechanisms for spin state changes, corresponding timescales as well as spin evolution due to outgassing torques are discussed. Different observational techniques and their pros and cons are presented together with the current status of cometary spin parameters for a variety of comets. The importance of rotation as an effective probe of the interior of the nucleus is highlighted. Finally, suggestions for future research aimed at presently unresolved problems are made.