Punishment involves deliberating harming individuals. How, then, if at all, is it to be justified? This, the first of three papers on the philosophy of punishment (see also ‘Punishment: Nonconsequentialism’ and ‘Punishment: The Future’), examines attempts to justify the practice or institution according to its consequences. One claim is that punishment reduces crime, and hence the resulting harms. Another is that punishment functions to rehabilitate offenders. A third claim is that punishment (or some forms of punishment) can serve to make restitution to victims, and a fourth is that it can strengthen social values. The paper examines these claims, and finally considers pluralist theories which combine retributive and harm-reductive or utilitarian considerations. (Retributive theories are examined in their own right in ‘Punishment: Nonconsequentialism’.)