  The principle of stationary variance is advocated as a viable variational
approach to quantum field theory. The method is based on the principle that the
variance of energy should be at its minimum when the state of a quantum system
reaches its best approximation for an eigenstate. While not too much popular in
quantum mechanics, the method is shown to be valuable in quantum field theory,
and three special examples are given in very different areas ranging from
Heisenberg model of antiferromagnetism to quantum electrodynamics and gauge
theories.
