The Social Contract, Or Principles of Political Right (1762) by Jean-Jacques Rousseau, is the book in which Rousseau theorized about social contracts as the origins of political community i.e. civil society.
Like John Locke, who believed that a government can only be legitimate if it has been sanctioned by the people in the role of the sovereign, Rousseau claimed that a perfect society would be controlled by the "general will" of its populace. While he does not define exactly how this should be accomplished (as there are many possible ways, each suited to different situations), he suggests that assemblies be held in which every citizen can assist in determining the general will. Without this input from the people, there can be no legitimate government. Importantly, this input cannot come from representatives, but must be from the people themselves.
— Excerpted from Wikipedia, the free encyclopedia.