The paper introduces SCAN (Strongly Constrained and Appropriately Normed) meta-GGA, a new density functional theory (DFT) method that satisfies all 17 known exact constraints for exchange-correlation functionals. Unlike previous meta-GGAs such as TPSS and revTPSS, SCAN is fully constrained and appropriately normed, making it highly accurate for systems where the exact exchange-correlation hole is localized near the electron, especially for lattice constants and weak interactions. SCAN is constructed to satisfy exact constraints and appropriate norms, including rare-gas atoms and nonbonded interactions. It is a nonempirical functional that achieves high accuracy without empirical parameters, and it is computationally efficient. SCAN is based on a semilocal functional form, which approximates the exchange-correlation energy as a functional of the electron density and its gradients. The functional is constructed to satisfy exact constraints, including uniform density scaling, spin-scaling, and the Lieb-Oxford bound. It also satisfies appropriate norms, such as the uniform density limit and the jellium surface energy. The SCAN functional is designed to be accurate for a wide range of systems, including atoms, molecules, solids, and surfaces. The SCAN functional is constructed by interpolating and extrapolating the exchange and correlation energy densities between different values of a dimensionless variable α, which represents the deviation from a single-orbital limit. The functional is designed to be accurate for both weak and strong bonds, and it is particularly effective for systems with long-range interactions such as van der Waals forces. The SCAN functional is also tested against a variety of benchmark sets, including the G3, BH76, S22, and LC20 sets, and it is found to be more accurate than other functionals such as PBE, TPSS, and M06L for many of these systems. The SCAN functional is implemented in a variety of computational methods, including ab initio molecular dynamics simulations, and it is used to calculate the exchange-correlation energy for a wide range of systems. The functional is also tested against experimental data, and it is found to be highly accurate for rare-gas atoms and nonbonded interactions. The SCAN functional is a significant improvement over previous functionals, and it is expected to be a valuable tool for a wide range of applications in materials science and chemistry.The paper introduces SCAN (Strongly Constrained and Appropriately Normed) meta-GGA, a new density functional theory (DFT) method that satisfies all 17 known exact constraints for exchange-correlation functionals. Unlike previous meta-GGAs such as TPSS and revTPSS, SCAN is fully constrained and appropriately normed, making it highly accurate for systems where the exact exchange-correlation hole is localized near the electron, especially for lattice constants and weak interactions. SCAN is constructed to satisfy exact constraints and appropriate norms, including rare-gas atoms and nonbonded interactions. It is a nonempirical functional that achieves high accuracy without empirical parameters, and it is computationally efficient. SCAN is based on a semilocal functional form, which approximates the exchange-correlation energy as a functional of the electron density and its gradients. The functional is constructed to satisfy exact constraints, including uniform density scaling, spin-scaling, and the Lieb-Oxford bound. It also satisfies appropriate norms, such as the uniform density limit and the jellium surface energy. The SCAN functional is designed to be accurate for a wide range of systems, including atoms, molecules, solids, and surfaces. The SCAN functional is constructed by interpolating and extrapolating the exchange and correlation energy densities between different values of a dimensionless variable α, which represents the deviation from a single-orbital limit. The functional is designed to be accurate for both weak and strong bonds, and it is particularly effective for systems with long-range interactions such as van der Waals forces. The SCAN functional is also tested against a variety of benchmark sets, including the G3, BH76, S22, and LC20 sets, and it is found to be more accurate than other functionals such as PBE, TPSS, and M06L for many of these systems. The SCAN functional is implemented in a variety of computational methods, including ab initio molecular dynamics simulations, and it is used to calculate the exchange-correlation energy for a wide range of systems. The functional is also tested against experimental data, and it is found to be highly accurate for rare-gas atoms and nonbonded interactions. The SCAN functional is a significant improvement over previous functionals, and it is expected to be a valuable tool for a wide range of applications in materials science and chemistry.