LAUSR

ABSTRACT This article explores the particular features of maritime border and migration controls and their differences to border enforcement on land. Drawing on how “classical” approaches to political geography, such as Friedrich Ratzel, viewed the differences between land and sea, and their impact on human activity, and using (mainly) examples of border control efforts in the Mediterranean, the following differences between controlling blue and green borders are highlighted: the heavier militarization of sea borders; the (inherent) nexus between border enforcement and migrant safety in the maritime domain; the more important role played by private commercial actors at sea; the “interstitial” nature of the maritime space, which brings with it more contention and uncertainty regarding states’ respective rights and duties in dealing with seaborne migration, and finally the generally “secondary” (or less essential) nature of maritime border controls compared to enforcing borders on land.