The article shows with what remarkable precision German diplomatic outposts, as well as consular agencies, scattered throughout Poland from Gdynia to Cieszyn to Lvov, gathered information about the Polish military potential. They used official materials, such as newspaper articles, Polish Armed Forces bulletins, as well information obtained from German citizens living in Poland and the ethnic German minority. The German military attaché who was also a member of the diplomatic staff in the German Embassy in Warsaw was in charge of the operation. The article reveals that in spring and summer of 1939, intelligence services stepped up their work. German diplomatic agencies in Poland were very helpful. Relations between Warsaw and Berlin were deteriorating and the initial distrust was replaced by open hostility. The article contains proof that agencies reporting to the German Foreign Ministry took part in drafting lists of Polish patriots to be deported or executed, as well Polish citizens of German nationality who were Nazi opponents. The Nazis later used these lists to track down and execute them. The article also explains what happened to the German diplomatic agencies in Poland in September 1939. It describes their evacuation by the Polish government to Lithuania and Romania, which was accompanied by some dramatic events, such as the possible assassination by the Polish military of the German consul in Krakow August Schillinger. The article also outlines the role played in Nazi-occupied Poland by German diplomatic agencies until the were closed down. The German Embassy in Warsaw was closed down in May 1940. German diplomatic and consular agencies on Polish territories provided essential information which enhanced the decision-making process within Nazi security agencies.