The challenging behaviours of people with intellectual disabilities do not exist in isolation from the social environment. Dominant causal models in the literature suggest a role for the actions of paid staff in service environments in particular. Central to these models is the hypothesis that staff may inadvertently behave in ways that serve to maintain challenging behaviour. In two papers, this dissertation seeks to enhance current knowledge of those factors held to influence the behavioural responses of direct care staff to challenging behaviours: (i) staff beliefs about client challenging behaviour, and (ii) staff affective reactions to the behaviour. The literature review paper provides a comprehensive account of research concerned with staff causal and intervention beliefs, negative emotional reactions and behavioural responses to challenging behaviour, with attention paid to pertinent methodological issues. The theoretical frameworks underpinning empirical enquiry are considered and, in particular, the empirical status of links between staff affect/cognition and actual caregiver behaviour is examined. The empirical paper utilises an interactive computer simulation of self-injurious behaviour with the aim of providing experimental evidence about the impact of beliefs and emotions on actual behaviour in situ. Participants with greater behavioural beliefs and less negative affect engaged in more habilitative behaviour when caring for a self-injuring 'child'. The results did not indicate any impact of either behaviourally inappropriate/inaccurate beliefs or raised negative affect on counter-habilitative staff behaviour likely to reinforce self-injury or other forms of challenging behaviour. A number of implications for research and clinical practice are discussed.