What does it mean to be disadvantaged? Is it possible to compare different disadvantages? What should governments do to move their societies in the direction of equality, where equality is to be understood both in distributional and social terms? Linking analytical philosophical theory with broad empirical studies, including interviews conducted for the purpose of this book, it is shown how taking theory and practice together is essential if the theory is to be rich enough to be applied to the real world, and policy systematic enough to have purpose and justification. The book is divided into three parts. Part 1 presents a pluralist analysis of disadvantage, modifying the capability theory of Sen and Nussbaum to produce the ‘genuine opportunity for secure functioning’ view. This emphasizes risk and insecurity as a central component of disadvantage. Part 2 shows how to identify the least advantaged in society even on a pluralist view. It is suggested that disadvantage ‘clusters’ in the sense that some people are disadvantaged in several different respects. Thus, it is not necessary to solve the problem of how to weigh different categories of disadvantage against each other in order to identify the least advantaged. Conversely, a society which has ‘declustered disadvantaged’ — in the sense that no group lacks secure functioning on a range of functionings — has made considerable progress in the direction of equality. Part 3 explores how to decluster disadvantage, by paying special attention to ‘corrosive disadvantages’ — those disadvantages that cause further disadvantages, and ‘fertile functionings’ — those which are likely to secure other functionings.