The term ‘marine protected area’ (MPA) refers to areas in which human activities that cause reductions in populations either directly through exploitation or indirectly through habitat alteration are eliminated or greatly reduced. This spatially explicit approach to managing human impacts has many potential ecological and socio-economic benefits that can alleviate some of the problems fundamental to conventional management practices and can therefore complement, but is unlikely to supplant, the conventional practices (Allison et al. 1998; Bohnsack 1998, Lauck et al. 1998; Hastings & Botsford 1999; Murray et al. 1999). Five reviews in this number of Environmental Conservation summarize the main issues relevant to MPAs in the Western Mediterranean, our understanding of their ecological and management consequences, and our knowledge of the ecological and socio-economic processes that determine their effectiveness for fisheries management and conservation (Badalamenti et al. 2000; García Charton et al. 2000; Pinnegar et al. 2000; Planes et al. 2000; Sánchez Lizaso et al. 2000). The reviews identify three issues of key importance to the development and success of MPAs for conservation and management. First, MPAs hold strong promise for management and conservation objectives, but the historical pattern of haphazard design, implementation, enforcement and evaluation has often produced equivocal and sometimes contradicting evidence for both their ecological effects and their effectiveness at achieving their intended objectives. Second, our understanding of many of the critical population and community processes that bear greatly on the consequences of this approach (e.g. dispersal, recruitment, direct and indirect effects of competition and predation) suffers from a lack of strong empirical studies and a comprehensive theoretical framework. Third, the global growth of interest in MPAs and concern for rapid development of organized systems of MPAs is great. Taken together, these three issues identify an urgent need for a well-developed theoretical framework, more rigorous empirical studies motivated and directed by theory, and actual implementation of systems of MPAs that will allow for proper evaluation and an evolution toward optimal design.