The manipulation of the electronic structure of low-dimensional materials has recently been the subject of active research with applications in spintronics, quantum information processing, energy storage, and novel composites. In particular, the electric conductivity of atomically thick materials such as graphene and black phosphorous yields an effective complex permittivity with a negative real part in the far- and mid-infrared spectrum. This feature allows for the propagation of slowly decaying electromagnetic waves, called surface plasmon-polaritons (SPPs), that are confined near the material interface with wavelengths much shorter than the wavelength of the free-space radiation. We will present theory, numerical methods, and computational results for surface plasmon-polaritons on conducting strips, edges, and layered materials. Joint work with Matthias Maier and Dio Margetis.