  We present a general method to study the non-equilibrium behavior of Casimir
type fluctuation induced forces for classical free scalar field theories. In
particular we analyze the temporal evolution of the force towards its
equilibrium value when the field dynamics is given by a general class of over
damped stochastic dynamics (including the model A and model B class). The
steady state force is also analyzed for systems which have non-equilibrium
steady states, for instance where they are driven by colored noise. The key to
the method is that out of equilibrium force is computed by specifying an energy
of interaction between the field and the surfaces in the problem. In general we
find that there is a mapping of the dynamical problem onto a corresponding
static one, and in the case where the latter can be solved the full dynamical
behavior of the force can be extracted. The method is used how to compute the
non-equilibrium Casimir force induced between two parallel plates by a
fluctuating field, in the cases of Dirichlet, Neumann and mixed boundary
conditions. Various other examples, such as the fluctuation induced force
between inclusions in fluctuating media are discussed.
