Growing demand for wireless spectrum has motivated research and development in underutilized or unused frequency bands such as the Terahertz frequencies (0.1-10 THz). With tens to hundreds of GHz-wide available bandwidth, the THz band can theoretically enable ultra high-bandwidth applications, such as virtual-reality video. The main challenges in THz-band communications are severe path loss caused by atmospheric absorption and low transmission power output due to small antenna size. In this dissertation, we propose a novel system architecture and algorithms to overcome these challenges and extend the effective transmission range of THz-band communications. First, we present a novel graphene-based plasmonic phased-array architecture where THz signals are directly generated and manipulated to form sharp beams. Next, we describe and propose a phase-only beamformer that maximizes the signal-to-interference ratio (SINR) and present a state-of-the-art polynomial-time approximate optimization algorithm. Then, we shift our focus to the problem of beam blockage and present a novel cooperative relaying system to extend transmission range as well as improve signal reception quality. Finally, for multimedia applications of THz-band communications (e.g. 3-D virtual reality content) we present a data embedding scheme that can augment the data rate further, while providing real-time media multiplexing capabilities and data confidentiality/security.