  In the framework of the Closed-Time-Path formalism, we show how topological
defects may arise in Quantum Field Theory as result of a localized
(inhomogeneous) condensation of particles. We demonstrate our approach on two
examples; kinks in the $2D \lambda \psi^{4}$ theory (both at zero and finite
temperature) and vortices in the complex $4D \lambda \psi^{4} $ theory.
