This paper describes elements in the social behaviour of the laboratory rat, mouse, hamster and Guinea-pig. These elements are divided into postures, which are static, and acts, which involve movement. A total of 45 of these elements are mentioned, most of which are common, with only slight modification, to all four species. Apart from these the guinea pig differs in not having a true Upright Posture and also in showing a male sexul display "Rumba". The postures are classified under broad motivational headings. A number of general concepts are discussed, for example the relation of convulsions to flight behaviour, the reduction of incoming aggressive stimuli in submissive postures, "Cut-Off", and the inhibition of biting in the more social species.