Shared decision making (SDM) involves patients and clinicians working together to reach a decision that is best for the patient. It is particularly important in the setting of incurable cancer, where it may be necessary to balance the risks and side effects of treatments with the benefits of increased survival or quality of life. Decision making conversations may include detailed discussions of complex information, and patients must be able to understand and process the information they have been given in order to weigh up the options. Health literacy (HL) plays a fundamental role in achieving SDM, yet is not always accounted for when interventions to support the process are developed. This PhD sets out to 1) explore and better understand the issues for SDM in incurable cancer, focussing on the particular challenges faced by those who experience difficulties with HL, and 2) identify the components of an intervention to support SDM in this setting. Guided by the Person Based Approach to Intervention Development, this Thesis describes four distinct phases of work carried out during the PhD study. They include a systematic review of the role of HL in cancer care, a series of interviews with patients diagnosed with incurable cancer suspected of experiencing difficulties with HL, an online survey of NHS healthcare professionals involved in decision making with patients with incurable cancer, and two expert panel meetings, one involving patients and carers and another with healthcare professionals. Findings from each phase informed the next and were ultimately synthesised and refined to form three overarching challenges for SDM in the context of incurable cancer and HL difficulties. These were used to devise of a set of guiding principles, from which a team based complex intervention to support SDM was developed. The overarching challenges identified for SDM in this setting included the persistence of traditional paternalistic clinician-patient roles, dealing with the emotional hurdles associated with a diagnosis of incurable cancer, and practical issues resulting from an imperfect system. A team based, complex intervention aimed at preparing patients, training teams and creating a supportive environment has been developed to overcome many of these barriers and improve SDM in this setting. Shared decision making is complex, and the emotional burden of an incurable cancer coupled with difficulties processing information make it all the more challenging to achieve in clinical practice. To better support SDM in this setting, it will be important to consider this combination of socio-cultural, emotional, and system-related barriers when developing future interventions.