Some people are worse off than others. Does this fact give rise to moral concern? Egalitarianism claims that it does, for a wide array of reasons. It is one of the most important and hotly debated problems in moral and political philosophy, occupying a central place in the work of John Rawls, Thomas Nagel, G. A. Cohen and Derek Parfit. It also plays an important role in practical contexts such as the allocation of health care resources, the design of education and tax systems, and the pursuit of global justice.

Egalitarianism is a superb introduction to the problem...