This chapter overviews applications of surface plasmon (SP) waveguides to advanced photonic devices/networks. The first topic introduces several configurations of diffraction-limit free compact SP waveguides. Notably, slot-type hybrid metal-insulator-metal (HMIM) and insulator-metal-insulator (HIMI) configurations exhibit SP field distributions mitigating deficient propagation length inherent to the SP waveguides, thus preferable for devices having features with both a size of an electronic device and a speed of a photonic device. The second topic is applications of hybrid SP waveguides to functional devices such as optical mode converter, modulator and detector with high-efficiency, high-speed, and broadband. They have a potential to function in the next-generation optical communication networks. The third topic is applications of the SPs to microwave plasmonics in wireless communications. SP devices positively challenge the high-speed and ultra-wideband demand in short optical links; optical interconnect in the sub-THz photonic world. 500 GHz plasmonic modulators with CMOS-processed Si photonics aggressively challenge the targets.