We study multiple light scattering from thermal fluctuations in the ordered phase of nematic liquid crystals. This state of condensed matter is characterized by long-range fluctuations of the local director, which are known to originate from bend, splay and twist deformations. This gives rise to a complicated polarization dependence of the "single-scattering" phase function, of which the consequences in multiple scattering will be discussed. In order to understand multiple scattering by long-range fluctuations in the dielectric constant, we first solve the Dyson and Bethe-Salpeter Equation for a scalar field amplitude in a self-consistent way. The diffusion constant is obtained numerically from the Kubo Greenwood formula. We compare the outcome with an approach based on point-like fluctuations. In the second part we take the tensorial aspects into account and solve the vector Bethe-Salpeter equation for light scattering caused by the De Gennes 1/q(2) Structure factor for the director fluctuations. Using a Kubo-Greenwood formula for vector waves, we calculate diffusion tensor and transport mean free path l* of the light. Due to uniaxial birefringence the transport mean free path is no longer given by the conventional Boltzmann formula l* = l(scal)/(1 - ). The consequences for the angular incoherent transmission (of the universal form (l*/L) (1/2 + 3 cos theta/4) will be investigated. Finally, we discuss the time-dependence of the thermal fluctuations in the context of the recent development of Diffusing Wave Spectroscopy initiated by Wolf and Maret.