In this chapter, we will begin by explaining the fundamental properties of the neutron, namely, its nature as a particle, its nature as a wave, and the fact that it possesses neutron spin. We will then compare the neutron’s energy with the interaction energy of matter. Furthermore, we will explain from their foundations the concepts of the differential scattering cross section, the neutron scattering length, and the scattering vector, which are essential for understanding scattering theory. Additionally, we will provide a clear explanation of scattering and absorption, coherent and incoherent scattering, and elastic and inelastic scattering.