Evidence suggests that the presence of positive emotions and the absence of negative emotions is beneficial. However, recent research shows that direct cognitive attempts to change how we feel can be counterproductive in the long run. Contextual Behavioural Science (CBS) based interventions, such as Acceptance and Commitment Therapy (ACT), limit direct attempts to change emotional states, and focus instead, on activating value-consistent behaviours. However, most measures used by CBS researchers and practitioners still focus on emotional states and reductions in symptomology, which may misfocus the client. Therefore, this thesis seeks to develop a practical, reliable, and valid measure of valued activity that can be used to guide intervention. The Six Ways to Well-Being (6W-WeB) measures the following six behaviours that are theorised to promote well-being: connecting with others, challenging oneself, giving to others, engaging in physical activity, embracing the moment, and caring for oneself. In addition, the 6W-WeB assesses the frequency of, and autonomous versus controlled motivation for, each behaviour. Study 1 focuses on the initial validation of the 6W-WeB in a sample of American adults (N1 = 1800, 60.3% female, Age: M = 40.9, SD = 13.21). Study 2 replicates the factor structure in an independent, Australian adult sample (N2 = 855, 47.3% female, Age: M = 38.16, SD = 13.35), and extends the research by assessing the barriers and enablers of valued action. Study 3 further replicates the validity of the questionnaire in two adolescent samples (N3 = 518, 100% female, Age: M = 14.29, SD = 1.46 and N4 = 185, 51.38% female, Age: M = 19.56, SD = 0.72) and tests the associations of 6W-WeB with personality traits and variables theoretically linked to each of the six behaviour domains. Study 4 combines the previously mentioned samples to maximise statistical power and test the factor structure of the 6W-WeB as well as its measurement invariance across countries, age groups, genders, and levels of psychological distress. Results indicate that the factor structure of the 6W-WeB is best represented by a bifactor confirmatory factor analysis (bifactor CFA) model, which consists of three global factors, namely behaviour engagement, activity importance, and activity pressure, as well as the six behavioural domain factors. This model showed good fit to the data and the items showed adequate internal consistency in all samples. Further, the findings suggest that the subscales of the 6W-WeB are linked in expected ways to theoretically-relevant measures, and that the 6W-WeB can differentiate between individuals who meet criteria for high psychological distress and those who do not. Finally, participants’ qualitative responses provided information about the specific ways through which they engage in the six behaviour domains, and the kinds of barriers that get in the way of valued action. Overall, the results indicate that the 6W-WeB may offer treatment utility for CBS practitioners, as the 6W-WeB is consistent with the core message of CBS – engaging in valued action may enrich and benefit one’s life. The new questionnaire, developed and validated in this thesis, can help orient clients towards activating value-consistent behaviour and allow clinicians to gain a deeper understanding of what their clients care about and love doing.