The Operational Zone of the Adriatic Littoral (German: Operationszone Adriatisches Küstenland, OZAK; or colloquially: Operationszone Adria; Italian: Zona d'operazioni del Litorale adriatico; Croatian: Operativna zona Jadransko primorje; Slovene: Operacijska cona Jadransko primorje) was a Nazi German district on the northern Adriatic coast created during World War II in 1943. It was formed out of territories that were previously under Fascist Italian control until its takeover by Germany. It included parts of present-day Italian, Slovenian, and Croatian territories. The area was administered as territory attached, but not incorporated, to the Reichsgau of Carinthia. The capital of the zone was the city of Trieste.

OZAK was established, with its headquarters in Trieste, on 10 September 1943, by Adolf Hitler, as a response to the Italian capitulation (8 September 1943) following the Allied invasion of Italy. It comprised the provinces of Udine, Gorizia [it], Trieste, Pula (Pola), Rijeka (Fiume) and Ljubljana (Lubiana). The Operational Zone of the Alpine Foothills, comprising the provinces of Belluno, South Tyrol, and Trentino, was established on the same day. Both operational zones were separate from the Italian Social Republic (RSI), based in Salò on Lake Garda, which governed the remainder of Italy that had not yet been occupied by the Allies.

The OZAK was not incorporated in the German Reich outright, but attached to the Gau of Carinthia. Friedrich Rainer, Nazi Gauleiter of Carinthia was appointed Reich Defense Commissioner of OZAK, thereby becoming chief of the civil administration of the semi-annexed territory. The province of Ljubljana was given a Slovenian provincial administration. Leading collaborator Gregorij Rožman, Bishop of Ljubljana, recommended to Rainer that notorious anti-Semite Leon Rupnik should be the president of the new Ljubljana provincial government, and Rupnik was then duly appointed on 22 September 1943. SS General Erwin Rösener became Advisor to the President.

OZAK was the scene of genocidal activities. Its commander, Higher SS and Police Leader Odilo Globocnik, had become one of the most feared Nazi leaders in Eastern Europe after liquidating the Jewish ghettoes in Warsaw and Białystok and supervising the operations of the extermination camps at Belzec, Sobibór, Majdanek, and Treblinka. He commanded all the Nazi camps in occupied Poland from 1941 to 1943. After serving briefly as Gauleiter of Vienna he had been posted to Trieste, where to the very end he ran the Risiera di San Sabba prison, the only SS camp ever set-up on Italian soil.

Globocnik, returning to his native city in triumph in mid-September 1943, established his office at Via Nizza 21 in Trieste and began to carry out Einsatz R, the systematic persecution of Jews, partisans and anti-Nazi politicians in Friuli, Istria and other areas of the Croatian Adriatic coastline. His staff of 92, mostly members of the German and Ukrainian SS with killing experience gained in Operation Reinhard, was quickly expanded to combat the unrelenting partisan activity throughout the region. Globocnik's domain included Risiera di San Sabba, a large, disused and decrepit rice mill at Ratto della Pileria 43 in the Triestine suburb of San Sabba. Under his supervision it was converted into the only Nazi extermination camp in Italian territory. The camp was used to detain hostages, partisans and political prisoners, and as a collection and transit camp for Jews being deported to Nazi concentration camps. In October 1943, arrests started and the camp opened, staffed primarily by German and Ukrainian members of the SS under the command of SS-Sturmbannführer Christian Wirth, former commander of Belzec extermination camp. Wirth was killed by Yugoslav Partisans in Opatija, on 26 May 1944. He was replaced by Wirth's former deputy in Lublin and successor in Belzec, SS-Hauptsturmführer Gottlieb Hering. Hering was replaced by SS-Obersturmbannführer Dietrich Allers in August 1944. On 28 April 1945, the San Sabba camp ceased operating, and Waffen-SS troops set free the remaining inmates and demolished the gas chamber and incinerator building the next day, to destroy evidence of war crimes.

Over 25,000 Italian, Slovene, Croatian and Jewish civilians passed through the San Sabba camp, about 5,000 were killed there by various methods including gassing. Today the rice mill is an Italian National Memorial Site. The camp's commanders and collaborators were tried in Trieste in 1976, but their sentences were never carried out.

The ethnic and political re-definition of the Adriatic Littoral was considered during the war on a theoretical level. In a telegram sent on 9 September 1943 to foreign minister Ribbentrop, Gauleiter Rainer suggests the future establishment of Reich protectorates in Gorizia, Istria and Carniola, based on the subdivisions of the Austrian-Hungarian Empire. Initial German occupation policy, however, favored incorporating the area into the Reichsgau of Carinthia. The ethnic complexity of the region was to be used to minimize Italian influence, promote ethnic segmentation, and introduce Germandom as a stabilizing force. This strategy was based on an understanding of history of medieval Germany and the Habsburg monarchy, where the German lords and nobles were seen to have made the economic and administrative development of the region possible.

The ethno-social composition of Venezia-Giulia, Trieste, and Friuli was an important component to Germany's plans of occupation. The fascist government had lost support of the fragmented social groups throughout the region- and the collapse of the regime ushered in a period of disorientation amongst Italians. Nazi propaganda worked to create the illusion that the areas under the zone had Austro-Hungarian roots. Germany had plans to adopt the region as part of the Reichstag; however, they used the region's imperial-past to make connections with the Austro-Hungarian Empire. They named the zone "Adriatisches Küstenland" which bore reference to the Austro-Hungarian past as that had been the name used by the empire in reference to areas North of the Adriatic. This propaganda relates to the greater German plan as they intended to replace Rome with Vienna as the capital of the region. Germans believed that by referencing the prosperous past, they could evoke feelings of nostalgia that would ultimately forge cultural links between Vienna and Trieste to Germany.