One of the best books on the subject is
L. Kadanoff, G. Baym, Quantum Statistical Mechanics
An original paper, which however has textbook quality and uses the Schwinger-Keldysh real-time contour formulation of non-relativistic off-equilibrium quantum field theory is the publication of Pawel Danielevic's PhD-Thesis:
Danielewicz, P.: Quantum Theory of Nonequilibrium Processes. 1, Ann. Phys. 152, 239, 1984
For the relativistic case and with extensions to off-shell transport, see the lecture notes by Wolfgang Cassing
Cassing, W.: From Kadanoff-Baym dynamics to off-shell parton transport, Eur. Phys. J. ST 168, 3–87, 2009
For a more general approach also for the relativistic case:
S. R. de Groot, W. A. van Leeuwen, Ch. G. van Weert, Relativistic kinetic theory