Over the last 40 years, marine protected areas (MPA) have been central to efforts to conserve marine ecosystems. This paper gives a brief history of the development of the MPA concept, and then reviews the various approaches that have been proposed to classify MPA according to their conservation objectives, uses, and geomorphological and oceanographical characteristics. Examples of MPA network development in Australia, the United States and Canada are examined. In the early 1970s, Australia became a pioneer in the establishment of MPAs. Work in California followed soon after, where outstanding cooperative efforts led to the adequate protection of 1000 km of its highly developed coastal zone. More recently, Canada started to work towards protecting its most fragile marine ecosystems, setting a 2020 goal for the protection of 10% of its marine waters. This paper gives special attention to the Saguenay–St. Lawrence Marine Park (Québec, Canada), which is seen as a unique example of collaboration between governments and local stakeholders. Key factors for successful implementation of MPA are examined in detail, and the lessons learned are highlighted.