Mathematical modeling, although a recent science, can be considered old when the time scale used to measure its age is the information technology evolution. FORTRAN 77 has been the most popular programming language among hydrodynamic modelers over the last two decades. This language was adequate to the (low) complexity of the models, limited by the exiting computers. The fast increase of the computing capacity allowed the development of more complex and multidisciplinary models. The necessity of new programming techniques became clear. It was started the era of the Object Oriented programming. Object Oriented programming isolates different parts of the code and allows communication among them using simple and robust interfaces. MOHID 2000 is an integrated modeling tool programmed in FORTRAN 95, using an Object Oriented strategy. It is the evolution of a set of models originally programmed in FORTRAN 77. Taking advantage of the new language possibilities, with a single code it is possible to perform different simulations (1D, 2D or 3D) and use a variety of vertical discretizations. This technique has also turned easy to integrate hydrodynamic, water quality, sediment transport and pollutants dispersion simulations using eulerian or lagrangian formulations. Having in mind the development of a tool accessible to the final user, the modeler must think about on the algorithms and code, but also on pre and post processing of the model data. MOHID 2000 input data files can be constructed by a graphical user interface. Output files use the standard HDF format making results exploring simple and allows the use of different graphic packages.