The d.c. and a.c. (2–17 cm −1 ) conductivities of InSe single crystals were measured for temperatures from 4.2 to 300 K. In the frequency range above 5 cm −1 for the polarization E ⊥ c, the submillimeter response of InSe is determined by free charge carriers, while at lower frequencies and in the d.c. limit additional effects of localization on potential barriers caused by imperfections of the crystal are observed. The average localization radius is evaluated. On the basis of our submillimeter data the “intrinsic” transport properties of charge carriers are determined, such as the mobility, the scattering rate, the concentration and the plasma frequency.