The seas have always posed a great challenge to humanity. This time, the challenge is not exploration or exploitation, but ensuring their sustainable use: this is the purpose of maritime spatial planning, which entails the design of the time and place of human activities at sea, an ambition that, as it should, is currently at the center of interest for the European Union, Greece, and many other countries.

Central themes of the book are the concept and content of spatial planning in general, and specifically maritime spatial planning and integrated coastal management. However, this requires a broader understanding of the marine space, the geography of oceans and seas, the characteristics of seawater, the institutional framework governing the seas, and the efforts for their regulation on an international, European, and Greek scale.

The initial chapters of the book are dedicated to the world's seas, focusing primarily on the regional seas of Europe – above all the Mediterranean – and Greece, while one chapter is dedicated to the law of the seas and the international treaties affecting the marine space, as well as the conventions regarding maritime zones, e.g., the continental shelf, exclusive economic zones, fishing protection zones, and issues related to environmental protection and sustainable development.

As the European Union Directive for Maritime Spatial Planning is integrated into our national law, it is essential to study in depth the EU's Integrated Maritime Policy, as well as all the parallel policies that influenced it. In this context, the evolution of EU directives is examined, as well as the international regulatory and protective experiences of European seas through intergovernmental agreements or via national initiatives from pioneering countries in this field.

Particular emphasis is placed on the Mediterranean, with a separate chapter dedicated to Greece and the efforts that are gradually leading to a coherent maritime spatial planning: the relevant institutional framework is presented, and special spatial frameworks are reviewed – even if some were abandoned or remained inactive – which directly or indirectly affect the marine regions of the country, e.g., for aquaculture, tourism, and coastal zones, renewable energy installations, and projects related to oil and natural gas.

At the same time, examples of marine parks for ecological protection, the issue of the shoreline and beach, initial exploratory efforts for maritime spatial planning, and the responsibilities of the state agencies involved are examined. The book concludes with a general synthesis and an outline of a first approach to maritime spatial planning in Greece, which could be functional and applicable until the difficult issues of delineating maritime zones, especially in the Aegean, are resolved.

The author's hidden desire is for the book not to be perceived as purely technocratic. The sea is not merely a technical object or pathetically ecological. It is the heritage of humanity, part of the subconscious of all of us, the liquid element that gave us life.