In this short chapter, associated with the Appendix A, we first establish the monokineticMonokinetic diffusion theory mathematical description. Such a relatively simple description has the great advantage of illustrating the balance between production, absorption, leakage and rate of change of neutron density without the complexity that is introduced by the treatment of important effects associated with the neutron energy spectrum and direction of the velocity vector. The neutron transport equation is a far more fundamental and exact description of the neutron population in a reactor than the neutron diffusion equation, and maybe easier to understand. The understanding of the transport equation provides a deeper and more thorough understanding of the diffusion theory and of the so-called “transport corrections”. This is sufficient reason for including an introduction to the transport equation in this elementary nuclear reactor book.