Critical human interests are affected on a daily basis by appeal to past decisions deemed to be ‘legally valid’. They include statutes, deportation orders, judgments, mortgage contracts, patents and wills. Through the technique of validity, lawyerly reasoning settles morally pressing matters in a way that largely bypasses moral argument. Legal philosophy has paid considerable attention to validity criteria, but it has neglected to explore validity’s point: whether, and if so how, the pervasive technique of validity can contribute to a legal system’s ability to realise justice and human rights. This book shows that validity can help a political community to foster justice precisely because validity does not primarily turn on moral considerations. Validity serves to both allocate, and limit, a distinct kind of power, a power that is key to forging valuable forms of enterprise and commitment in pursuit of individual and collective self-direction. By entrusting the capacity to decide to those who, in justice, ought to bear it, validity can enable persons and institutions to rally the resources and opportunities that only large-scale behavioural convergence can afford, thereby weaving a fabric of just relationships within the systemic framework of law.