This chapter’s purpose is to present the aim of the book, its rationale, focus, approach and the basic concepts necessary to make sense of what follows. The first part outlines the aim and approach, focussing on the impact of diet on the human brain and mind, alongside an outline of the content. The second part provides an overview of the core knowledge and methods that underpin research into diet, brain and mind. This starts with basic nutritional (energy needs, macronutrients, micronutrients) and physiological concepts (metabolism, digestion, regulation). It then covers the key issue of dietary measurement (self-report, observation, biomarkers, manipulation) and its limitations (accuracy, demand, stability over days and decades). The latter part examines the measurement of mind and brain – and its limitations – concentrating, respectively, on neuropsychological tests and imaging approaches. The final part describes our study inclusion criteria, and our rationale for favouring those with a whole diet focus.