Terahertz (THz) technology bridges the gap between electronics and photonics, unlocking transformative opportunities in medical diagnostics, molecular identification and next-generation wireless networks. Usually, THz devices have been made from conventional semiconductors and their heterostructures to achieve the necessary carrier transport properties and optical-to-THz conversion efficiencies. In the past decade, carbon nanomaterials, such as carbon nanotubes and graphene, have been successfully used in the development of THz devices, including emitters, detectors and modulators. These advances are enabled by the unique properties of these materials, including strong linear and nonlinear THz radiation absorption, ultrahigh carrier mobilities and facile gate tunability. In this Review, we present the latest advances in the generation, detection and modulation of THz radiation using carbon nanomaterials, particularly focusing on the use of carbon nanotubes and graphene. The challenges and opportunities of using carbon nanomaterials in THz technology and towards potential applications are discussed.