Resumen
European Union law has decisively influenced the development and recent evolution of national legislation on environment and on public procurement. One of the most important objetives of European Directives on public procurement have been to introduce environmental protection. But the principles of objectivity, transparency, publicity and non discrimination must be respect in all cases. These principles constitute at present the foundation of all public rules on procurement and are characterized by their transversality as they cover and are manifest in all stages of the contract, preparation and performance.