Underwater cultural heritage (UCH) constitutes an invaluable asset, which is lately being challenged by the blue growth trend that cannot be easily reconciled with the goal of UCH preservation and promotion. Maritime spatial planning (MSP)—under a place-based approach—creates better chances for UCH to receive more attention in the future compared to other resources, since it is considered to be the key procedure for tackling growing competition among sea users (user-user conflicts) and for mitigating the pressure these users put on the marine environment (natural and cultural). In Greece, a country with great insularity, extensive marine space, and a long and glorious past, UCH resources are in abundance. According to the official Ministry of Culture data-base, there are 88 designated UCH sites throughout the national waters, the majority of which are found very close to the shore. They usually concern ancient cities and built monuments that were eventually submerged (due to earthquakes, geological processes, etc.), so they usually have a mixed nature—terrestrial and marine. These sites, however, constitute a very small part of what is actually lying on the Greek seabed. Estimations for the future identify a rise in accidental discoveries of UCH, due to the blue growth trend and an increase in access to and work in the sea. In this event, much controversy is expected, concerning the appropriate type of management for UCH. The role of MSP in this decision-making process will be decisive, being about “when” and “where” human activities take place at sea, to ensure these are as efficient and sustainable as possible.