Advances in experimental techniques allow investigating extremes of dynamics of particles in interaction with electromagnetic field. The theoretical tools at disposal are classical and quantum mechanics and the experience show that it is dangerous to dismiss one (classical) at the expense of the other (quantum): each one has merits that should be fully explored. The problem, however, is to bridge the gap between them so that the information they give is complementary and not contradictory. In the book this goal is achieved by formulating five postulates, and level of their implementation distinguishes the two mechanics. Dynamics of particles (charges) is not complete without unifying it with the dynamics of electromagnetic field, which in the book is given special emphases.