Along with recent fundamental changes in several aspects of the port industry, ports come up against formidable environmental challenges. It is thus important and often imperative to mainstream environmental concerns in their operation, planning, and development; improve their environmental performance; and make the transition to sustainable production and consumption patterns. The industry’s greening is largely underpinned by European Union (EU) transport and port policy, with major European initiatives such as the Trans-European Transport Network (TEN-T), the European Green Deal, and Blue Growth expected to give new impetus. This paper examines environmental mainstreaming in Greek TEN-T ports and their ability to cope with upcoming challenges based on questionnaire responses by 23 port authorities and taking into account the relevant progress made by ESPO port members. We argue that all respondents have gradually become aware of the need to move towards an environment-friendly operation and development, but progress is slow, and there is still a lot to be done. Performances vary and depend on different factors, while ports are faced with significant challenges and various constraints. Nevertheless, new environmental standards present a real opportunity for Greek ports to undertake deep structural changes, especially in view of current and future European port policy.