This chapter presents some plasmonic waveguides devices. First, a plasmonic grating made of a two-dimensional (2-D) metal-insulator-metal (MIM) waveguide is analyzed with attention to its propagation characteristics. It is shown that the grating acts as a band stop filter with relatively large sidelobes. To reduce the sidelobes, an apodized grating is introduced into the filter. It is found that the sidelobes are effectively suppressed, leading to a step like band stop property. In addition, a plasmonic microcavity is analyzed, in which a defect section is introduced into the band-stop filter. Next, the performance of MIM waveguide-based band-pass filters is investigated, in which the results from 2-D model are compared with those from three-dimensional (3-D) one. It is revealed that the performance from the 2-D waveguides cannot be obtained by simply adopting the 3-D ones. Finally, the rod waveguides are efficiently analyzed using the cylindrical and body-of-revolution (BOR) FDTD methods. The formulation of the LOD-BOR-FDTD method is given and the reflection characteristics of the rod waveguide are presented.