Abstract: This Handbook entry presents a conceptual, normative overview of the subject of taxation. It emphasizes the relationships among the main functions of taxation - notably, raising revenue, redistributing income, and correcting externalities - and the mapping between these functions and various forms of taxation. Different types of taxation as well as expenditures on transfers and public goods are each integrated into a common optimal tax framework with the income tax and commodity taxes at the core. Additional topics addressed include a range of dynamic issues, the unit of taxation, tax administration and enforcement, and tax equity.