Reich Foreign Office
Under the Weimar Republic and Nazi Party, the Reich Foreign Office was the cabinet ministry concerned with the conduct of diplomacy. It was headed by Foreign Ministers Constantin von Neurath (1932-1938) and Joachim von Ribbentrop (1938-1945).
The Foreign Office is generally accepted to have had a role in German expansion by means other than war, but the conventional wisdom had been that it was much less important after the 1939 outbreak of war, and the diminishing power of Ribbentrop. A recent report released by the current German Foreign Ministry, however, reveals that it was significantly involved in planning and directing Holocaust. Ribbentrop's personal assistant, Gustav Adolf Steengracht von Moyland, testifying in his defense, minimized its role.
The foreign policy, not only on its basic lines, but also usually down to the most minute details, was determined by Hitler himself. Ribbentrop frequently stated that the Fuehrer needed no Foreign Minister, he simply wanted a foreign political secretary. Ribbentrop, in my opinion, would have been satisfied with such a position because then at least, backed by Hitler's authority, he could have eliminated partly the destructive and indirect foreign political influences and their sway on Hitler. Perhaps he might then have had a chance of influencing Hitler's speeches, which the latter was accustomed to formulate without Ribbentrop, even in the foreign political field. 
It was the only agency that had an authority and duty to advise that a proposed government action would violate international law.
Between 1921 and 1936, it was organized much as other foreign ministries: departments organized by geographic region, and specialist departments (i.e., personnel & administration, legal and cultural). On 15 May 1936, it was reorganized into the structure it would generally maintain until 1945; changes were to personnel, not organization.
The regional bureaus were organized into a Political Department, and all units dealing with economic matters were put into a Trade Affairs Department. In addition, there were three more coequal departments: administration & personnel, law and culture. There were also press and protocol offices, and a Subdepartment Germany.
Although the Foreign Office may have had an unsuspected and significant role in Holocaust, a common belief is that by 1943, Ribbentrop concluded that he would not have a major role in foreign policy, and replaced a number of civil servants with Sturmabteilung members and Gauleiters. Other civil servants gained promotion because they were Party members. Ribbentrop promoted Gustav Adolf Steengracht von Moyland to permanent personal assistant after a 1943 reorganization in which he replaced many career diplomats, such as Ernst von Weizsaecker, Ernst Woermann and Friedrich Gaus, put presumably more loyal professionals (Andor Hencke, Erich Albrecht and Emil Wiehl) in the Political, Law and Trade Departments, and his own loyalists in all other new posts.
Also in 1943, Undersecretary Martin Luther attempted, backed by Heinrich Himmler and the SD, to replace Ribbentrop. Himmler withdrew support after deciding Luther would be even worse, and Luther, whom Ribbentrop had recruited when Luther ran a furniture moving service, was sent to Sachsenhausen Concentration Camp.
A number of diplomats were involved in the 20th of July Plot and were purged.
Role in German expansion before war
Ernst von Weizsaecker, then head of the Political Department, issued a 10 November 1937 memorandum explaining Hitler's criteria for a modus vivendi with Britain. "...we want colonies and freedom of action in the East. The British need for tranquility is great It would be profitable to find what England would be willing to pay for such tranquility." The Foreign Office, however, had not participated in a 5 November 1937 member with Hitler and the senior military, discussing contingency plannng for war. His exact role in the transition remains controversial. While Shirer did not consider him a completely reliable source, at the end of the war, he was the only surviving witness to discussions between President Paul von Hindenburg and Adolf Hitler. 
Von Weizsaecker was aware of the Czech crisis in May 1938, writing that the Western press had humiliated Adolf Hitler in suggesting that he had called off his invasion of Czechoslovakia: "Hitler had embarked on no military enterprise, and thus could not withdraw from one. But unfortunate provocation from the foreign press really set Hitler going. From then on, he was emphatically in favor of settling the Czech question by force of arms."
Advice for war
Woermann helped fabricate prewar border incidents with Poland. 
In October 1941, von Weizsaecker advised that Poland not be categorized as occupied territory, which would make international law applicable, "to which we doubtless shall not submit." 
According to Eckart Conze, professor of modern history at the Philipps University of Marburg and one of the authors of the report,"The sheer scale of the participation of Germany's Foreign Ministry in the Holocaust is bewildering. It wasn't just one department; it was the whole institution. The ministry collaborated with the Nazis' violent policies and took part in all aspects of the discrimination, deportation, persecution and genocide of the Jews."
While SS ranks for civil servants often were honorary, Joschka Fischer, the former foreign minister who started the study made the general observation, “The sentence that shocked me the most described how the co-operation between the foreign ministry and the [SS] was so close that the boundaries became fluid.” 
In 1940, Franz Rademacher, head of the Jewish Desk, sent a memorandum to State Secretary Martin Luther, asking him to define Foreign Minister Joachim von Ribbentrop's basic policy toward Jews, trying to shift the role of his desk from settling individual cases to establishing policy.  He also originated the Madagascar Plan proposal for deporting all European Jews to Madagascar.
Rademacher, along with Luther, received reports, from Reinhard Heydrich, on Einsatzgruppen killings. His assistant, Fritz Gebhard von Hahn, summarized them. Summaries from both Hahn and Luther went to Ernst von Weizsaecker and Ernst Woermann, who circulated them to interested parties in the Foreign Office. The summaries were initialed by 16 officials. 
Postwar legal precedent
The Ministries Case (NMT) ruling on the Foreign Office has been argued to have set precedent for criminal prosecution of lawyers who give illegal advice, an issue that has been raised with respect to interrogation methods and extrajudicial detention.
- Nuremberg Trial Proceedings Vol. 10, NINETY-FIRST DAY, Tuesday, 26 March 1946, Morning Session, at 106-108
- Hans-Adolf Jacobsen (1999), The Structure of Nazi Foreign Policy 1933-1945, in Christian Leitz, The Third Reich: the essential readings, Wiley-Blackwell, pp. 56-57
- Leitz, pp. 62-63
- William Shirer (1960), The Rise and Fall of the Third Reich, Simon & Schuster, pp. 302-304
- Peter Maguire (2001), Law and War: An American Story, Columbia University Press, p. 161
- John Toland (1976), Adolf Hitler, Doubleday, p. 464
- Shirer, p. 214
- Tristana Moore (27 October 2010), "Were German Diplomats Complicit in the Holocaust?", Time
- Derek Scally (25 October 2010), "German diplomats 'complicit in Holocaust'", Irish Times
- Christopher R. Browning (2004), The Origins of the Final Solution: The Evolution of Nazi Jewish Policy, September 1939-March 1942, University of Nebraska Press, ISBN 0-8032-1327-1, p. 82
- Browning, pp. 83-88
- Browning, pp. 491-492
- Kevin Jon Heller, "Want to Prosecute the Lawyers? Cite Ministries — Not the Justice Case", Opinio Juris