A Theory of Justice is a book of political philosophy

Political philosophy

Political philosophy is the study of such topics as liberty, justice, property, rights, law, and the enforcement of a legal code by authority: what they are, why they are needed, what, if anything, makes a government legitimate, what rights and freedoms it should protect and why, what form it...

 and ethics

Ethics

Ethics, also known as moral philosophy, is a branch of philosophy that addresses questions about morality—that is, concepts such as good and evil, right and wrong, virtue and vice, justice and crime, etc.Major branches of ethics include:...

 by John Rawls

John Rawls

John Bordley Rawls was an American philosopher and a leading figure in moral and political philosophy. He held the James Bryant Conant University Professorship at Harvard University....

. It was originally published in 1971 and revised in both 1975 (for the translated editions) and 1999. In A Theory of Justice, Rawls attempts to solve the problem of distributive justice

Distributive justice

Distributive justice concerns what some consider to be socially just allocation of goods in a society. A society in which incidental inequalities in outcome do not arise would be considered a society guided by the principles of distributive justice...

 by utilising a variant of the familiar device of the social contract

Social contract

The social contract is an intellectual device intended to explain the appropriate relationship between individuals and their governments. Social contract arguments assert that individuals unite into political societies by a process of mutual consent, agreeing to abide by common rules and accept...

. The resultant theory is known as "Justice as Fairness", from which Rawls derives his two famous principles of justice: the liberty principle and the difference principle.
In A Theory of Justice, Rawls argues for a principled reconciliation of liberty

Liberty

Liberty is a moral and political principle, or Right, that identifies the condition in which human beings are able to govern themselves, to behave according to their own free will, and take responsibility for their actions...

 and equality

Equality before the law

Equality before the law or equality under the law or legal egalitarianism is the principle under which each individual is subject to the same laws....

.