This book contributes to the description of electronic structure and transport in metallic CNTs with electrode contacts. DFT coupled with NEGF theoretical approach has been applied to different electrode materials. Ballistic transport calculations are based on the nonequilibrium Green's function formalism combined with density functional theory (DFT). A systematic investigation of different contact materials is carried out using suitable atomistic metal-CNT-metal structures, optimized in an appropriate way. Based on the models, electronic transport calculations are carried out, which further can be extended to large systems by applying the DFT calculator. Transmission spectrum and differential conductance are useful results to investigate the CNT-metal interaction and its influences on the transport. Horizontal, vertical and angular configurations are compared that may be suitable for future on-chip interconnect applications. Antenna and sensors are designed and fabricated based on the application of carbon nano-materials. With a development and an increasing interest in flexible electronics, the design of a patch antenna is presented using CNT-polymer ink on fabrics.