The chapter reviews the theory of phase ordering dynamics, focusing on recent developments. It emphasizes the scaling regime that emerges at long times after a system is quenched from a homogeneous phase into a broken-symmetry phase. The chapter discusses how to determine the growth laws that describe the time dependence of characteristic length scales and the form of associated scaling functions. Particular attention is given to systems with more complex order parameters, such as vector and tensor fields, which are necessary for describing phase ordering in nematic liquid crystals. The study of topological defects (domain walls, vortices, strings, monopoles) provides a unifying framework for understanding coarsening in various systems. The chapter is organized into several sections, covering dynamical models, scaling hypothesis, domain walls, nonconserved and conserved fields, growth laws, and the Lifshitz-Slyozov-Wagner theory. It also discusses binary liquids and the role of advection in their phase separation. The chapter concludes with a discussion of exact results for short-distance singularities and scaling functions, as well as universality classes for phase ordering dynamics.The chapter reviews the theory of phase ordering dynamics, focusing on recent developments. It emphasizes the scaling regime that emerges at long times after a system is quenched from a homogeneous phase into a broken-symmetry phase. The chapter discusses how to determine the growth laws that describe the time dependence of characteristic length scales and the form of associated scaling functions. Particular attention is given to systems with more complex order parameters, such as vector and tensor fields, which are necessary for describing phase ordering in nematic liquid crystals. The study of topological defects (domain walls, vortices, strings, monopoles) provides a unifying framework for understanding coarsening in various systems. The chapter is organized into several sections, covering dynamical models, scaling hypothesis, domain walls, nonconserved and conserved fields, growth laws, and the Lifshitz-Slyozov-Wagner theory. It also discusses binary liquids and the role of advection in their phase separation. The chapter concludes with a discussion of exact results for short-distance singularities and scaling functions, as well as universality classes for phase ordering dynamics.