The Member States of the European Union (EU) have developed various means of preventing irregular migration. Those Member States along the Mediterranean coast find themselves under increasing pressure to control immigration effectively. In response, they have begun externalising their border controls and, in cooperation with European Union Agency for the Management of Operational Cooperation at the External Borders (FRONTEX), intercepting and repatriating migrants caught at sea. EU Member States, including Spain, have entered into bilateral agreements with African states such as Cape Verde in order to enter and conduct interception operations in the latter’s territorial waters. Is Spain duty-bound and, if so, to what extent is it duty-bound to extend human rights and refugee law protection to those it intercepts at sea pursuant to the Spanish-Cape Verdean bilateral agreement and during FRONTEX operations? This thesis will explore Spain’s practice and the law concerning interceptions on the high seas and in the territorial waters of Cape Verde. What are Spain’s duties, if any, during these operations? The thesis will discuss the extraterritorialisation of jurisdiction and argue that Spain does indeed have jurisdiction and duties, including those concerning human rights and non-refoulement, towards persons it intercepts at sea.