The theory of planned behaviour, social identity theory and attitudes toward institutional authority were used to predict the uptake of outreach services over a 3-week period in a prospective study of 126 homeless people in a major UK city. Consistent with previous research, subjective norm was an important predictor, but so were identification with support services and attitudes to authority. The effect of intention on behaviour was moderated by subjective norm, such that intention affected behaviour more when subjective norm was weak. Subjective norm was affected by identification with support services, which in turn, was predicted by identification with homeless people and attitude to authority. It is concluded that the role of social identity and social norms is of central importance in understanding uptake of outreach services among homeless people. (Authors)