Background: Palliative care professionals work with ongoing emotionally and practically challenging situations. These challenges may include dealing with complex symptomology, being unable to relieve suffering, patient deaths, and having to have difficult end-of-life conversations with patients and their family members. Despite these challenges, palliative care professionals appear to have similar or lower levels of occupational stress or burnout compared to other medical professional groups (e.g. oncology, medical-surgical, etc.). The current thesis had three main aims. Firstly, it was hoped that this research could lead to better decisions around measuring occupational stress in palliative care professionals. Second, this research aimed to describe and understand the experiences of palliative care professionals and the helpful and unhelpful ways they respond to stress or challenges at work. Thirdly, this thesis hoped to explore the role of psychological flexibility (i.e. ability to contact the present moment without judgment while persisting or changing behaviour in accordance with chosen values) in the wellbeing of palliative care and other healthcare professional wellbeing. Fourthly, this thesis also aimed at further investigating the psychometric properties of the Mindful Healthcare Scale (MHS; Kidney, 2017), a new measure of psychologically flexible helping. To address these aims the research in this thesis made use of multiple research methodologies including a systematic review, a qualitative framework analysis study, and a longitudinal survey design. Study 1 method and results: The first study was a systematic review of occupational stress measures used with palliative care professionals; it also aimed to investigate psychological predictors of occupational stress in this population. In this review, the COSMIN was used to rate the quality of the studies with respect to the psychometric properties being addressed in each study. The results indicated that Maslach Burnout Inventory, Professional Quality of Life Scale, and Nursing Stress Scale were the most widely used measures and had the most evidence to support their use with palliative care professionals. However, based on the COSMIN criteria the methodological quality of the studies was fair overall. In addition, a narrative review of the psychological predictors of occupational stress was provided. A number of psychological factors identified as protective (e.g. self-efficacy/competence, professional social support) and harmful (e.g. psychiatric morbidity, deathrelated anxiety) for palliative care professional wellbeing. Overall, this review implies that the methodological quality of studies in this area could be improved particularly by making hypotheses more explicit, reporting missing data information, and using more longitudinal designs to examine responsiveness and test-retest reliability of measures. Study 2 Method and Results: A qualitative framework analysis study was used to describe and understand the experiences of palliative care professionals and how they responded in helpful or unhelpful ways to challenges at work. Semi-structured interviews were conducted with 9 employed palliative care professionals. Participants identified being able to make a difference to the suffering of others and personal growth as sources of meaning and purpose in their work. Participants also highlighted emotional challenges in providing palliative care, difficult patient family dynamics, work environment factors (e.g. caseload), uncontrollability of patient symptoms, having goals blocked and public perceptions of palliative care work as stressful as frustrating aspects of their work. They also noted areas in which this work had a personal impact such as making them more clear about life priorities and being more comfortable with death and dying. In addition, a number of helpful (e.g. accepting of challenges, being present) and unhelpful (e.g. self-doubt, lack of self-care) responses were explored in relation to their wellbeing and performance at work. This study provides further understanding of the experiences of palliative care professionals and has some implications for the design of interventions/training programs for this population. Study 3 Methods and Results: This study was a longitudinal survey study of palliative care provision, general psychological flexibility (i.e. Comprehensive Assessment of Acceptance and Commitment Therapy processes [CompACT]; Francis et al., 2016), psychological flexibility in healthcare providers (MHS), self-compassion, self-as-context, and empathy in predicting wellbeing in healthcare professionals. Participants were recruited through social media (e.g. twitter posts with a link to the study), contacting Marie Curie Hospices in Scotland, and word of mouth. Participants who completed survey at time point 1 (T1; N = 163) were invited by email to take part in the survey at time point 2 (T2; N =83). Data from T1 were used to examine the structural validity of a new measure of psychological flexibility in healthcare work (Mindful Healthcare Scale [MHS]; Kidney, 2017) and to conduct a cross-sectional analysis of the relationships between the psychological predictors and the wellbeing outcomes. Data from T2 was used to examine the predictive ability of the psychological predictors measured at T1 and wellbeing outcomes measured at T2. A confirmatory factor analysis (CFA) approach and an exploratory structural equation modelling (ESEM) within CFA (EwC) approach were used to examine the structural validity of the MHS and its subscales (Engaged, Awareness, and Defusion) in healthcare professionals. ESEM is a less restrictive approach compared to CFA and allows for the cross-loadings of items. Of the 163 participants recruited at T1 one participant was excluded for having incomplete MHS response leaving 162 participants in the analysis. Two measurement models were tested: (1) The original MHS model [Higher order factor: PsychFlex. Firstorder factors: Engaged (5 items), Awareness (5 items), and Defusion (3 items)] (2) a one factor model [i.e. all items loading onto psychological flexibility], Results from these analyses suggested that the ESEM approach outperformed the CFA approach in terms of model fit for the original model but not for the one-factor model. Furthermore, the original model as analysed using the EwC approach was the only model that reached satisfactory fit; the CFA approach to the original model did not reach a satisfactory fit. The onefactor model was not considered to have satisfactory fit in either CFA or ESEM analyses. These findings suggest that the original model of the MHS is a robust measurement of psychological flexibility in healthcare professionals. It also suggests that the MHS may be best conceived as a multidimensional measure of psychological flexibility with items loading onto more than one factor. The cross-sectional survey data at T1 were used to examine the role of psychological flexibility in predicting wellbeing and burnout in healthcare professionals. Based on correlational analyses, psychological flexibility (both the generic and healthcare specific measure) appeared to positively correlate with general wellbeing and compassion satisfaction and negatively correlated with burnout and secondary trauma. However, the defusion subscale of the MHS only significantly and negatively correlate with secondary trauma. In hierarchical regressions, it was revealed that the subscales of the MHS added significant additional variance in the prediction of the outcomes over and above the subscales of the CompACT. However, the defusion subscale only contributed to additional variance in secondary trauma. Palliative care and non-palliative care providers differed on the fantasy subscale of the empathy measure but not on any other measures. The longitudinal data (including both T1 and T2) were used to examine the ability of psychological flexibility to predict wellbeing outcomes in healthcare professionals at a six-month follow-up. The MHS total score, engaged subscale, and awareness subscale positively correlated with general wellbeing and compassion satisfaction and negatively correlated with burnout. However, only the awareness subscale and total scale negatively correlated with secondary trauma. Defusion was found to only be significantly correlated with compassion satisfaction but in the negative direction (r = -.27, p < .05). Therefore, a revised MHS was explored in further analyses (Revised MHS = Engaged + Awareness; i.e. without defusion). The revised subscale correlated in expected directions with all outcomes. In terms of incremental validity across time, the revised MHS explained additional variance for compassion satisfaction and burnout over and above the CompACT. However, it did not add additional variance for general wellbeing or secondary trauma across the six-month interval These findings also suggest that psychological flexibility can predict future wellbeing and burnout outcomes in healthcare professionals. The longitudinal data was also used to examine the test-retest reliability of the MHS. Based on the Intraclass Correlation Coefficients (ICC) the testretest reliability of the original MHS (ICC = .77, p < .001), defusion subscale (ICC = .78, p < .001) and the revised MHS (ICC = .80, p < .001) were considered good; whereas the engaged subscale (ICC = .73, p < .001) and awareness subscale (ICC = .71, p < .001) were considered moderate. Therefore, the MHS appeared to have moderate-to-good test-retest reliability. Future research should extend this finding and examine the responsiveness or sensitivity to change of the MHS.