The Physical Internet (PI) is a relatively young and compelling vision about the freight transport and logistics system of the future. Besides showing how many technological and organizational innovations could converge in a real-world logistics system, it also addresses cross-industry interests such as digitalization, standardization, resilience, and environmental sustainability. In the logistics R&D community, the PI is already inspiring new designs of loading and packaging material, architectures for collaboration, and open information exchange, as well as algorithms for system-wide optimization. Our focus is on the position and role of maritime ports within the PI, as the transport hubs that facilitate most of the world's international trade. We introduce the key notions of the PI vision and expand on the unique position of maritime ports in the PI with the respective challenges this may create. Finally, we discuss the requirements for maritime ports to be ready to take up their role in the PI. We found that policy directions for ports to contribute to the development and implementation of the PI lie within the areas of transport infrastructure, (PI) standardization, advanced terminal areas, ICT hardware, information systems (IS) and platforms, and sustainability management.