This paper reviews recent advances in emission and detection of terahertz (THz) radiation using two dimensional (2D) plasmons in semiconductor heterostructures and their applications. The device structure is based on a high-electron mobility transistor (HEMT) incorporating the asymmetrically interdigitated dual-grating gates (ADGGs). Its excellent THz emission and detection performances are experimentally demonstrated by using fabricated InP-based ADGG HEMTs. Their arrayed monolithic integration and module assembly/packaging issues are also discussed. Finally their applications to THz sensing and wireless communications are demonstrated.