The Enlightenment was an intellectual movement in the 18th and 19th centuries characterized by belief in reason and human rights. It challenged old traditions and promoted scientific thought. Key thinkers included John Locke, who identified natural rights like life, liberty, and property, and Montesquieu, who advocated for separation of powers in government. The Enlightenment had social, political, and economic impacts including increased criticism of social stratification and revolutions separating governmental powers.