This chapter presents a review of the current state of technology regarding certain aspects of such reservoirs. Physical properties of fractures and fractured systems are defined and discussed. Various flow processes and models describing these processes are reviewed. Particular emphasis has been placed on the imbibition flow process.Experimental results on imbibition in carbonate chalk are presented. A large number of samples have been tested in the laboratory, and the results are discussed in regard to effects of wetting properties, sample shapes, and boundary conditions. Simulation of one of the experiments shows that the prediction of imbibition flow rate by simulation models is critically dependent on a well defined capillary pressure curve.An improved dual porosity model for simulation of multiphase flow in fractured reservoirs is discussed. 554