Switzerland’s representation of US diplomatic interests in Cuba is the most enduring protecting power mandate in history. After the break of official relations between Washington and Havana in January 1961, the Swiss authorities took over American interests on the Caribbean island and continue to do so until today. A substantial change of the mandate occurred in September 1977 with the establishment of the so-called “United States Interests Section of the Swiss Embassy in Havana”. It enabled the return of American officers to their embassy in the Cuban capital in order to take care of administrative matters, on the basis of reciprocal rights for the Cubans in Washington. Today, the Swiss flag still flies on top of the US embassy building in Havana, but the Swiss Head of Mission in Cuba only intervenes in matters of principle or in exceptional circumstances. It was the period between 1961 and 1977 when the Swiss clearly faced the most challenging times with their mandate for the US in Cuba. The documents available so far show that the mandate at the time included a number of exceptional tasks beyond the classic obligations of a protecting power, and that the Swiss were repeatedly involved in direct negotiations with the Cuban leader Fidel Castro over a number of issues between Washington and Havana.