The analysis of coastal and marine ecosystems is a complex issue. The paper suggests that the policy analysis undertaken to appraise the an environmental project, policy or programme, should be supported by an ecosystem services approach for the valuation of ecosystem services and benefits. The use of such an approach for coastal and marine Mediterranean ecosystems is examined. Although constrained by uncertainties surrounding scale and spatial issues, and the nonlinearity and thresholds problem, a valuation of the Mediterranean Sea benefits can be undertaken. This can form an important component of a decision support system guided by sustainability objectives.