In times of increasing environmental awareness, the port-city relationship has gained a new meaning since ports have been seen as the origin of both negative and positive externalities affecting the public wellbeing. While the former are the result of port expansion, the latter are the result of transforming obsolete port areas into recreational facilities. Therefore, in order to support effective policy-making, in this research is emphasized the need of measuring these environmental externalities. Considering their non-market nature, the contingent valuation method is introduced as an economic tool capable of overcoming this obstacle. Thus, the cases of two ports in Spain, namely Valencia and Castellón, are reviewed. The policy implications of this are discussed with the aim to improve the understanding of the changing relationship between ports and cities.