This dissertation offers an ethnographic account of life for people with a brain tumour. It explores their understandings of disease and attempts to secure treatment amid progressive and unpredictable bodily decline. It asks how these people negotiate changing relationships with families and cope with their own emotional struggle and self-doubt as the effects of tumour manifest. It also examines how these people's lives are shaped by medical institutions and the changing formations of care. Above all, it is a study of navigation which explores how people with a brain tumour imagine and enact trajectories for their lives under conditions of radical change-bodily and institutional. From October 2014 to May 2016, I undertook fieldwork at a hospital I call The Warner-a publicly-funded specialist hospital for people with neurological disease in the UK. Over these eighteen months, I interviewed and conducted long-term participant observation with sixteen people with a brain tumour to understand their lived experiences and approaches to medical decision-making. I worked intensively with thirteen of these people and their families as they struggled to understand their condition and plot the best course through care and treatment amid the shifting protocols of NHS administration, scientific knowledge and ailing bodies. I also worked intensively with healthcare professionals, observing routine practice across multiple settings including clinics, multidisciplinary team meetings, laboratories and radiology departments, and interviewing them about their work. Building on an analytic of social navigation (Vigh 2007; 2009), my ethnography brings into view the multiple temporalities of a constantly shifting terrain of disease, care and treatment. Rather than examining scientific innovation, clinic contexts, and patient experience independently, I argue that studying the interactions between them is critical for understanding the condition of patients and their relations with families and clinicians as they live through disease and navigate care.