There are several international and European legal instruments which provide a legal basis for the establishments of marine protected areas (MPAs) for the purpose of improving fishery management in the marine environment. Nevertheless, the effectiveness of MPAs remains open to debate and considerable attention is now focussed at international and European levels on how to improve the enforcement of regulations in MPAs. In this context, there is little doubt but that monitoring, control and surveillance (MCS) are indispensable tools for improving law enforcement and compliance in such areas. Indeed, recent experience in the European Union suggests that the effectiveness of MCS ought to be a primary consideration when designated areas to be protected in the marine environment. Accordingly, the aim of this article is to focus on some of the difficulties that must be overcome in order to improve the effectiveness of MCS in MPAs. Particular emphasis is placed on the problems that stem from the absence of common definitions regarding the characteristics of the area to be protected, the absence of harmonisation of MCS in such areas, as well as the problems that stem from practical considerations such as the size, shape and location of MPAs. The article also reviews basic fishery enforcement measures which can improve the effectiveness of MPAs including: hydrofencing, special fishing permits, one gear rule, as well as specific monitoring systems and security enforcement zones. Although the total harmonisation of regulatory measures is desirable from a law enforcement perspective, the article nonetheless concludes that it is also possible to have specific MCS solutions tailored to meet the characteristics of the area that needs to be protected.