This review updates a previous one published two years ago, focusing on recent progress in thermoelectrics, including advances in charge and heat carrier transport, strategies to improve the figure of merit (ZT), and new discussions on device physics and applications. Understanding phonon transport in bulk materials has advanced significantly with first-principles calculations and experimental tools. New strategies have been developed to improve electron transport in thermoelectric materials. Fundamental questions about phonon and electron transport across interfaces and in thermoelectric materials remain. With ZT values exceeding one, the field is ready to move beyond materials' figure of merit. Developing device contacts, module fabrication techniques, efficiency measurement platforms, and identifying applications are increasingly important for the future of thermoelectrics. The review discusses advances in carrier transport, including phonon and electron transport. Phonon transport in bulk materials has seen significant progress with first-principles calculations and simulations. Phonon mean free paths (MFPs) are still uncertain, and experimental methods to determine them are challenging. Interfaces in nanostructured materials introduce additional complexity, and thermal boundary resistance (TBR) is a significant factor. Theoretical models for TBR are limited, and numerical methods like molecular dynamics and Green's function approaches are being used to improve understanding. Electron transport is complex, and the Seebeck coefficient and electrical conductivity are important for optimizing the thermoelectric power factor. The electronic band structure of thermoelectric materials is calculated using first-principles methods, but band gaps are often underestimated. More sophisticated methods like GW and Bethe-Salpeter equations are being used to improve accuracy. Electron mobility is influenced by impurity and phonon scattering, and first-principles calculations are challenging due to the complexity of the systems. Strategies for the next generation of nanocomposites include energy filtering at interfaces, which can enhance the Seebeck coefficient and power factor. Resonant impurity levels in the conduction or valence band can also enhance the Seebeck coefficient. Nanoparticles in alloys can scatter phonons more efficiently than electrons, improving ZT. The choice of nanoparticle material is crucial, and factors like work function and band offset determine their effectiveness. The review highlights the importance of understanding these factors to improve thermoelectric performance.This review updates a previous one published two years ago, focusing on recent progress in thermoelectrics, including advances in charge and heat carrier transport, strategies to improve the figure of merit (ZT), and new discussions on device physics and applications. Understanding phonon transport in bulk materials has advanced significantly with first-principles calculations and experimental tools. New strategies have been developed to improve electron transport in thermoelectric materials. Fundamental questions about phonon and electron transport across interfaces and in thermoelectric materials remain. With ZT values exceeding one, the field is ready to move beyond materials' figure of merit. Developing device contacts, module fabrication techniques, efficiency measurement platforms, and identifying applications are increasingly important for the future of thermoelectrics. The review discusses advances in carrier transport, including phonon and electron transport. Phonon transport in bulk materials has seen significant progress with first-principles calculations and simulations. Phonon mean free paths (MFPs) are still uncertain, and experimental methods to determine them are challenging. Interfaces in nanostructured materials introduce additional complexity, and thermal boundary resistance (TBR) is a significant factor. Theoretical models for TBR are limited, and numerical methods like molecular dynamics and Green's function approaches are being used to improve understanding. Electron transport is complex, and the Seebeck coefficient and electrical conductivity are important for optimizing the thermoelectric power factor. The electronic band structure of thermoelectric materials is calculated using first-principles methods, but band gaps are often underestimated. More sophisticated methods like GW and Bethe-Salpeter equations are being used to improve accuracy. Electron mobility is influenced by impurity and phonon scattering, and first-principles calculations are challenging due to the complexity of the systems. Strategies for the next generation of nanocomposites include energy filtering at interfaces, which can enhance the Seebeck coefficient and power factor. Resonant impurity levels in the conduction or valence band can also enhance the Seebeck coefficient. Nanoparticles in alloys can scatter phonons more efficiently than electrons, improving ZT. The choice of nanoparticle material is crucial, and factors like work function and band offset determine their effectiveness. The review highlights the importance of understanding these factors to improve thermoelectric performance.