The Lorentz-Mie theory of the extinction and scattering of light by small spherical particles is applied to soot particles in flames. Extinction and scattering coefficients and angular scattering patterns are calculated, in the visible range, for different values of the complex refractive index of soot. Theoretical results for the emissivity and dispersion of the extinction coefficients are presented for monodisperse and polydisperse systems.