As semiconductor devices become smaller, the temporal and spatial scales become sufficiently short and the electric field sufficiently large that new physical constraints are reached in treating the transport of carriers within the devices. These devices are now controlled by strong size‐related effects: coupling to the environment of contacts, interfaces/boundaries/surfaces, interconnects, and other devices. This is especially the case in MOSFET’s, where remote interface phonons and surface roughness scattering dominate the transport. In this talk, a general treatment of device–environment interaction will be discussed. Special cases for MOS transport and the specific role of interfaces will be treated.