This chapter examines Hugo Grotius' key political ideas. Grotius, one of the most prolific and erudite writers of the seventeenth century, sought to formulate a set of universal rights and duties that would secure peace by constraining states in their internal and external relations. Drawing on a wide range of philosophical and literary sources, including Roman law, ancient classics, theology, and poetry, Grotius rehabilitated the natural law in an attempt to achieve harmony in an increasingly splintered political environment. After providing a short biography of Grotius, the chapter analyses his views on natural law, natural rights, property rights, sociability, self-preservation, and social contracts. It also discusses Grotius' arguments regarding international order in the context of just war theory and punishment and concludes with an assessment of Grotius' legacy in the area of political thought.