In the introduction to his Political Liberalism, John Rawls summarizes what he considers to be five fundamental features that are required in order for a democracy to be stable, just, and viable. In many ways Rawls is a fairly traditional left-liberal political thinker, but his work is uncommonly concerned with the role that the basis and structure of society has on the social outcomes that we deem just or unjust. Rawls is part of the Kantian tradition in moral and political philosophy, and thus occupied with trying to balance the twin goals of building a just and equal society society (which might be construed as an expression of Kant's dictum that one should do only what one might consent to as a universal principle of action) and the maintenance of the freedom and dignity of all persons in that society (Kant's dictum that persons should never be treated merely as means to an end).
These twin goals are reflected in Rawls in the pursuit of social justice without compromising the principle that the consent and concerns of those affected by policies that lead to social justice are relevant to the discussion. One way to give a quick and dirty summary of Rawls' project is to say he wants to improve the lot of the worst off without undervaluing the freedoms of the well off. Rawls manages to simultaneously annoy Marxists and Libertarians, which, to me, is an indicator that he's on to something.