Abstract: The thermoelectric effect is an eco-friendly energy technology that can directly convert heat into electricity, or vice versa. It is hoped that thermoelectric generators based on the Seebeck effect can alleviate the energy crisis. A brief overview of the development of mediumtemperature p- and n-type thermoelectric materials is presented. The pros and cons of candidate thermoelectric material systems for electricity generators are considered, while the research opportunities and challenges are highlighted to promote future potential applications.