Trichotillomania (hair pulling disorder) can be a debilitating mental health condition, but current interventions are not without their flaws. Central to developing an effective intervention is to first accurately measure it. Thus, this thesis’ first aim was to develop an assessment instrument for trichotillomania, with the intention to build an intervention. Traditional assessment measures for trichotillomania ignore the importance of the situation, can lead to inaccuracies, and may not give a complete picture of pulling for each individual. Chapter 2 addresses these concerns and builds a novel assessment instrument for trichotillomania, based on the theory of grounded cognition. Our results created a detailed pulling profile for each individual that was situation specific and presented promising areas for interventions to focus on. The second aim of this thesis was to develop an intervention for trichotillomania. As part of this intervention, we were interested in social connectedness and social support and what role they may play in hair pulling, given their association with mental health in general. Chapters 3 and 4 therefore develop an assessment instrument for social connectedness and social support, again building from the theory of grounded cognition. Findings from these studies helped to develop our understanding of influential processes for social connectedness and social support, and situational effects. Finally, the Discussion chapter introduces a trichotillomania intervention developed from the previous studies and the wider literature and further discussed the implication of the findings within Chapters 2-4.