The book investigates the political thought of Algernon Sidney (1623-1683), a historical character of the English civil wars, republic, protectorate, and Rump Parliament, who faced his trial and execution during the Exclusion Crisis. In his writings, Sidney mixed hugely different traditions of political philosophy: the modern natural rights, which were predominant in England in his generation, and the republicanism of Machiavelli. This volume will interest researchers in political philosophy, history of political thought and, particularly, republican theory. Its contribution to these topics explores the specificities of a thought that uses the language of natural rights and social contract and, on the other hand, the tumults, expansion and virtues of the republics.