Variational expansions in quantum chromodynamics

The results obtained in the last few years using nonperturbative variational expansions in quantum chromodynamics are reviewed. The review begins with examples which explain the method of constructing variational series in quantum field theory, along with how the properties of their convergence can be controlled by special parameters. The variational perturbation theory for quantum chromodynamics is then formulated, and a nonperturbative expansion in a new small parameter is constructed. Various phenomenological applications of this approach are discussed.