We present a tight-binding (TB) model and k·p theory for electrons in monolayer and few-layer InSe. The model is constructed from a basis of all s and p valence orbitals on both indium and selenium atoms, with tight-binding parameters obtained from fitting to independently computed density functional theory (DFT) band structures for mono- and bilayer InSe. For the valence and conduction band edges of few-layer InSe, which appear to be in the vicinity of the Γ point, we calculate the absorption coefficient for the principal optical transitions as a function of the number of layers, N. We find a strong dependence on N of the principal optical transition energies, selection rules, and optical oscillation strengths, in agreement with recent observations D. A. Bandurin et al., Nat. Nanotechnol. (2016). Also, we find that the conduction band electrons are relatively light (m∝0.14–0.18me), in contrast to an almost flat, and slightly inverted, dispersion of valence band holes near the Γ point, which is found for up to N∝6.