[en] The self-consistent method in quantum field theory is discussed. It is shown that this method is particularly suitable to the study of ordered states like the ferromagnetic and superconducting states. In both systems, the symmetry of the Heisenberg fields is rearranged, due to the dynamics of the system, to a different symmetry at the level of observation. For example, the spin rotation of electrons in a ferromagnet is induced by the E(2) symmetry transformation of quasielectrons and magnons. Dynamical rearrangement of symmetry in a ferromagnet is studied in detail by using the path integral technique in field theory. The reason for rearrangement of symmetry is shown to be the infrared effect. This calculation is rigorous and holds for the itinerant electron ferromagnet and the localized spin model. The itinerant electron ferromagnet is studied as a specific model by applying the self-consistent method in field theory. The magnon as a bound state is studied by using the Bethe--Salpeter equations in the pair approximation. The dynamical rearrangement of symmetry is studied. The self-consistent method when applied to superconductivity has been called the boson method. The magnetic properties of pure Type-II superconductors at T = 0⁰K are studied by using this method. An improvement over the previous preliminary analysis is presented by using the exact shape of the boson characteristic function. The normal cores at the center of the vortices are taken into consideration. Detailed analysis of the phase transition at H/sub c1/ is presented. Numerical calculations of H/sub c1/, H/sub c2/, kappa/sub c/, kappa/sub cr/ and equilibrium lattice length d₀, are given