Display omitted •Systematic fundamental summary of thermoelectric coolers (TECs).•Detailed overview of TEC design, from materials to device engineering.•Deep theoretical understanding-based TEC performance discussion.•Pointing out the future research direction of TECs. Traditional cooling technologies, employing cooling refrigerants, have caused severe ozone depletion and global warming. Alternatively, thermoelectric coolers, with the advantages of emission-free, noise-free, and environmentally friendly, have attracted extensive research interest and shown great application potential. Here, to render a systematic review on thermoelectric coolers, we firstly discuss the application potential from battery cooling to microchip cooling, and then summarize the key parameters to evaluate performance of thermoelectric coolers. After that, material suitability and device engineering strategies with enhanced performance are systematically overviewed from the physics, chemical, and material fundamentals. Finally, we point out the future directions of thermoelectric coolers from materials manufacturing to device design. This review can render systematic understanding and guidance to the cooling performance optimization and application field expansion of thermoelectric coolers.