In this chapter magnetohydrodynamical (MHD) equations are derived from the Boltzmann equation. First, we discuss under what conditions particle systems can be treated as magnetohydrodynamical systems. Next, the set of magnetohydrodynamical equations are derived from the Boltzmann equation by taking the moments of the equation. In this derivation of MHD equations, we examine ion and electron systems separately, because it is instructive to see the origin of electromagnetic force on fluid. Generalized Ohm’s law is also derived. In this chapter gravitational force is neglected for simplicity.