Background: This thesis describes a three-year mixed methods study which aimed to develop and test the feasibility of an exercise intervention for people who are surgically treated for lung cancer. The study employed the Health Action Process Approach (HAPA) as an underpinning theoretical framework in order to focus on the behaviour change components necessary for such kind of intervention. It used an inductive approach to aid the development of the intervention using guidance from the Medical Research Council (MRC) on developing and evaluating complex interventions. Methods: The study was split into two phases with three parts. Phase one part one consisted of a systematic review examining the literature on exercise intervention for people who are surgically treated for lung cancer. Part two comprised a qualitative study examining the attitudes and beliefs of key stakeholders (patients and health professionals) on exercise for the population under study. The results from phase one informed the development of a three week pre-surgical exercise intervention carried out in phase two. Feasibility and acceptability were measured alongside other secondary outcomes to explore the feasibility of implementing the intervention. Results: The results from the review illustrated the infancy of the field under study and provided evidence for the need for further investigation of key stakeholders’ attitudes and beliefs. The qualitative study, which included 23 participants, added to the results from the review and indicated that the design of an exercise intervention for this population should be multifaceted, for example including the option for both supervised centre-based group exercise and home-based exercise such as walking. Fourteen participants were recruited to the three week pre-surgical exercise intervention implemented in phase two. The results concerning feasibility of the intervention designed were mixed. Overall recruitment rate was low (33%). However, at one participating site recruitment was much higher (63%) and overall adherence to the programme was acceptable (74%) for those who did attend. The intervention was considered acceptable (measured through individual interviews), participants reported enjoying the programme and wanting to continue with something similar after their surgery. Participants felt the intervention should be part of standard care. Concerning secondary outcomes, the only statistically significant change detected was improvement in exercise capacity measured by 6MWT (p=0.018, median 50 metres) from baseline to post-intervention. Conclusion: A review of the literature and exploration of key stakeholders’ attitudes and beliefs towards exercise for people surgically treated for lung cancer provided a strong evidence base for a multifaceted exercise intervention to be designed. The intervention proved to be feasible under certain circumstances (e.g. where there was sufficient time before surgery) and acceptable by people who opted to participate. Future pilot and RCT work is necessary in order to develop the intervention further and test the feasibility, acceptability and effectiveness of implementing it into clinical practice.