The fundamental properties of a plasma depend upon the interactions between the plasma particles and the existing force fields. These fields may be externally applied or they can be internal fields associated with the nature and motion of the particles themselves. In this text the words collision and interaction are used synonymously. The notion of a collision as a physical contact between bodies loses its utility in the microscopic world. In the atomic level a collision between particles must be regarded as an interaction between the force fields associated with each of the interacting particles.