The light water high conversion reactor is aimed at the extension of standard pressurized water reactor technology toward better fuel utilization. This can be achieved by mechanical spectrum hardening via tightening the fuel rod lattice of the core. Its main merits will be a high conversion ratio, high discharge burnup, and long fuel cycles. The ongoing investigations in reactor physics, thermohydraulics, emergency core cooling, and fuel technology have shown so far that the basic design is feasible, but they have also indicated that it might, under certain circumstances, be advantageous to widen the lattice somewhat to increase safety margins, e.g., with respect to the void coefficient.