The estate of French maritime ports (“grands ports maritimes”, formerly known as “ports autonomes”) is subject to the public domain regime. This special legal regime is used to protect the allocation of properties that are considered to benefit a public interest. Since the 1990s, the public domain regime for port estate has been made more flexible in order to encourage private investments, and thus the development of port areas. This article does not aim to analyse these changes from a legal point of view but from a spatial planning point of view. The objective is to underline the fact that they contribute to redefining the role of port authorities as port land managers and developers. Their intervention is no longer subordinated to their role as public infrastructure managers. They now have the possibility to exercise their competences for commercial purposes. This orientation questions and even weakens the principle of public interest which legitimates the role of port authorities as land managers and developers.