During the past 10 years, the evolution of marine spatial planning (MSP) and ocean zoning has become a crucial step in making ecosystem-based, sea use management a reality. The idea was initially stimulated by international and national interest in developing marine protected areas, e.g., the Great Barrier Reef Marine Park. More recent attention has been placed on managing the multiple use of marine space, especially in areas where conflicts among users and the environment are already clear, e.g., in the North Sea. Even more recent concern has focused on the need to conserve nature, especially ecologically and biologically sensitive areas, in the context of multi-use planning of ocean space. Despite academic discussions and the fact that some countries already have started implementation, the scope of MSP has not been clearly defined. Terms such as integrated management, marine spatial management, and ocean zoning are all used inconsistently. This is one of the reasons why its importance is not more seriously reflected at the levels of policy and decision-making in most countries. This article attempts to deal with this problem. It describes why MSP is an essential step to achieve ecosystem-based sea use management, how it can be defined and what its core objectives are. The article concludes with an analysis of the use and achievements of MSP worldwide, with particular focus on new approaches in Europe.