Advanced plans were made by the Dutch government to extend the port of Rotterdam by means of the construction of a land reclamation in the North Sea, the Maasvlakte 2. Because no safety standards exist for the Maasvlakte 2, it is useful to determine an optimal design from an economic point of view by cost-benefit analysis. The economic optimal design of the Maasvlakte 2 is assumed to be the design for which the net present value (NPV) of the total costs (including loss of benefits) is minimal. An accompanying optimal level of safety for the Maasvlakte 2 is also found. In this analysis, the Maasvlakte 2 is assumed to be a system composed of three elements, a breakwater, a sea defence and a terrain area. For each element, decision variables are selected which have influence on the resistance (strength) and the costs and benefits of the Maasvlakte 2, and also represent relations between elements. For the breakwater, the crest height and the diameter of the concrete blocks in the armour layer are considered as decision variables. For the terrain area, the height of the terrain area is the only decision variable considered. For the sea defence, the crest height, the diameter of the quarry stones in the protection layer of the outer slope and the angle of the outer slope are considered as decision variables. A selection of failure modes is also made for each element.Each failure mode is written in the form of a reliability function Z = R-S in which R is the resistance and S is the sollicitation. For the failure modes, hydraulic conditions (waves, water levels) represent the sollicitation. The geometry and strength of the elements, also determined by the decision variables, represent the resistance. In the calculation of the economic optimal design of the Maasvlakte 2, a bottom-up approach is used: 1. at first, calculations are executed for each failure mode 2. then, these results are used in the optimisation per element 3. finally, optimal element results are used in the optimisation of the system. This way the optimal design for Maasvlakte 2 is derived. With this optimisation method, a probabilistic design is determined and compared with a deterministic design it proves to be much more cost effective.