Thermoelectric generators that convert thermal energy into electrical energy through thermoelectric materials have attracted considerable attention recently, because of their potential use in various applications. Using this technology, electricity can be generated from waste heat. However, the only practically usable thermoelectric material currently available is Bi2Te3. Thus, the development of other thermoelectric materials that have a high performance and are safer is necessary. Although most thermoelectric materials are alloys and ceramics, in recent years, organic materials have also been explored for use as flexible thermoelectric materials. The thermoelectric characteristics of various carbon materials, in particular, carbon nanotubes, have also been reported. In this paper, we review the fundamentals of thermoelectric power generation. In addition, we also review and discuss the results of studies on the thermoelectric properties of carbon materials such as graphite, carbon nanotubes, graphene, composites, and graphite intercalation compounds.