This colloquium provides an overview of recent theoretical and experimental progress in the nonequilibrium dynamics of isolated quantum systems, with a focus on quantum quenches. Quantum quenches involve the sudden or slow change of coupling constants in the system Hamiltonian, leading to temporal evolution that can be studied in both gapped and gapless systems. The colloquium discusses the universality of slow dynamics near quantum critical points and in generic gapped and gapless systems, emphasizing the importance of adiabaticity and the scaling behavior of various quantities such as defect density and heat with the quench rate. It also reviews recent progress on thermalization in closed systems through the eigenstate thermalization hypothesis and relaxation in integrable systems. Experimental progress in cold atom systems is discussed, highlighting the comparison between theoretical models and experimental observations. The colloquium concludes by outlining key open questions and future directions in the field.This colloquium provides an overview of recent theoretical and experimental progress in the nonequilibrium dynamics of isolated quantum systems, with a focus on quantum quenches. Quantum quenches involve the sudden or slow change of coupling constants in the system Hamiltonian, leading to temporal evolution that can be studied in both gapped and gapless systems. The colloquium discusses the universality of slow dynamics near quantum critical points and in generic gapped and gapless systems, emphasizing the importance of adiabaticity and the scaling behavior of various quantities such as defect density and heat with the quench rate. It also reviews recent progress on thermalization in closed systems through the eigenstate thermalization hypothesis and relaxation in integrable systems. Experimental progress in cold atom systems is discussed, highlighting the comparison between theoretical models and experimental observations. The colloquium concludes by outlining key open questions and future directions in the field.