Wellbeing has many differing definitions, facets, concepts, and dimensions. It can mean different things to different audiences. While the lay term wellbeing may be considered to mean feeling happy and positive, psychologists may argue that the concept also comprises life satisfaction, purposefulness, and meaning, while in the health context, wellbeing may be considered the absence of symptoms of psychological distress, such as anxiety and depression. This lays the foundations for difficulty in how we communicate about wellbeing and how we measure and evaluate it, but we must if we are to build an evidence base for heritage interventions that can be used by service commissioners, providers, and policy makers. This chapter provides an overview of the theoretical foundations of wellbeing, as well as discussing what is meant by mental health, and explains the ways in which wellbeing can be quantified and measured, as well as discussing ways in which we may evaluate wellbeing through qualitative methods.