The contiguous zone is notorious for being the most poorly defined international maritime zone. Confusion about exactly what enforcement operations can lawfully be conducted by coastal States against foreign ships in the zone has existed from its creation in 1958. Uncertainty about the full legal character of the contiguous zone has long been recognised as a shortcoming, leading to it being the most poorly utilised maritime zone by coastal States with little more than half of the 167 States Parties to the 1982 United Nations Convention on the Law of the Sea (LOSC) claiming the zone. The most difficult aspect about the contiguous zone is the scope of the unique preventative powers that may be exercised by coastal States within it, which are limited to four ill-defined topic areas in Article 33 of LOSC (customs, fiscal, immigration and sanitary). This chapter examines the contiguous zone and considers the extent to which it can be utilised by coastal States for environmental protection purposes. A complication in determining the potential utility of the contiguous zone to assist coastal States to combat environmental threats and in encouraging State practice to develop in this regard, is that the zone overlaps the exclusive economic zone (EEZ), in which coastal States have ability to engage in activities to protect and preserve the maritime environment. The key issue is whether the contiguous zone powers enable a fuller suite of actions to be taken in order to protect the environmental interests of the coastal State.