The sea and space are comparable environments. They share certain characteristics: vastness, absence of physical obstacles and the immense freedom of manoeuvre they offer. This article attempts to show that those who use the sea have found the answer to many of their needs in space-based solutions: communications, navigation, meteorology, oceanography, surveillance, etc. Space can also play a federating role in the major projects that Europe needs in the maritime aspects of the security, scientific and environmental fields.