We shall be concerned with the role of intercarrier scattering in hot carrier systems. The intercarrier scattering within a band acts to drive the carriers towards a displaced Maxwellian distribution. In so doing it alters both the energy distribution and the angular distribution in momentum space. Hence we recognise two facets of the scattering, namely momentum transfer and energy transfer between the carriers. In low-field transport the momentum transfer influences the mobility in an indirect manner by altering the angular distribution and this changes the momentum loss to the lattice by the other scattering mechanisms. This effect is important at high carrier densities and its presence should be signalled by a dependence of mobility upon density but in practice it is necessary to allow for accompanying changes in other factors such as impurity scattering. If there are several species of carrier, momentum transfer by inter-band scattering will occur and this has a direct effect upon mobility because of the difference in effective mass of the interacting carriers. For example, in electron-hole scattering, momentum is usually lost from the electrons to the holes in a manner similar to the momentum loss to stationary ionized impurities. This topic of intercarrier scattering in low-field transport had been extensively explored by the early 1960’s.