This review discusses the recent progress in developing high-performance thermoelectric (TE) materials with a dimensionless figure of merit (ZT) and the fabrication processes for nanostructured materials. The challenge in enhancing TE performance is to tailor the interconnected physical parameters—electrical conductivity, Seebeck coefficient, and thermal conductivity—of a crystalline system. Nanostructures offer opportunities to decouple thermal and electrical transport by introducing new scattering mechanisms. Recent improvements in TE efficiency have focused on reducing lattice thermal conductivity through nanostructural design. The review covers materials such as Bi–Te alloys, skutterudite compounds, Ag–Pb–Sb–Te quaternary systems, half-Heusler compounds, and high-ZT oxides. It also discusses future strategies for developing TE materials, including band structure engineering and exploring new materials with complex crystalline structures. The review highlights the potential routes for improvement in major TE material systems and the significance of nano-engineering strategies in enhancing TE performance.This review discusses the recent progress in developing high-performance thermoelectric (TE) materials with a dimensionless figure of merit (ZT) and the fabrication processes for nanostructured materials. The challenge in enhancing TE performance is to tailor the interconnected physical parameters—electrical conductivity, Seebeck coefficient, and thermal conductivity—of a crystalline system. Nanostructures offer opportunities to decouple thermal and electrical transport by introducing new scattering mechanisms. Recent improvements in TE efficiency have focused on reducing lattice thermal conductivity through nanostructural design. The review covers materials such as Bi–Te alloys, skutterudite compounds, Ag–Pb–Sb–Te quaternary systems, half-Heusler compounds, and high-ZT oxides. It also discusses future strategies for developing TE materials, including band structure engineering and exploring new materials with complex crystalline structures. The review highlights the potential routes for improvement in major TE material systems and the significance of nano-engineering strategies in enhancing TE performance.