Direct internal reforming molten carbonate fuel cell (MCFC) systems an generally more efficient and more simple than equivalent external reforming systems. It is demonstrated that even better performance and system simplicity can be achieved by connecting the stacks in networks with the cathode Bows and/or anode flows in series. The advantages and disadvantages of such networks are presented. Within the EC＇s Joule III programme, stack networking has been explored for direct internal reforming-molten carbonate fuel cell (DIR-MCFC) systems. This study resulted in the selection of a system which employed anode recycle with the anodes connected in parallel and the cathodes connected in series. It achieved high performance, yet required few system components. In the project ＇Advanced DIR-MCFC development＇, led by BCN (P. Kortbeek and R. Ottervanger, J. Power Sources, 71 (1-2) (1998) 223), this system is being assessed with regard to cost, operating window, and controllability. The approach is to design the system to conform to the requirements of ECN＇s stacks. At the same time the MCFC stack development at ECN (G. Kraaij et al., J. Power Sources, 71 (1-2) (1998) 215) is geared towards fulfilment of the requirements in such a system with respect to performance, pressure management and lifetime, so the development of the system and the stack have an iterative character. A novel, patented, stack design with two anode outlet streams has been proposed by BG. It can be used in the chosen system and gives increased power output.