The present diploma thesis aims to build an optimization model that will allocate in the best possible way a constrained budget for the upgrade of the 12 most important Greek Passenger Ports. On that purpose, mathematical models are developed based on the principles of the linear integral programming. These mathematical models are solved through an objective function, which includes two distinct parameters that depict the importance of those 12 Greek passenger ports and the infrastructure projects, chosen to be implemented for their upgrade. Having as a constraint the initial available budget, the objective function needs to be maximized during the optimization process and 10 different optimization scenarios are solved in total and the results of their solutions are synthesized so that useful conclusions can be drawn. From the models it was derived that the parameters having a non-linear impact to the optimum project budget distribution are the budget size, the projects’ cost, the investments’ escalation and the ports and activities assessment coefficients. It was found that the return brought to the ports from the projects is not increasing proportionally with the increase of the available funds.