The Ordnungspolizei (Orpo, German: [ˈɔʁdnʊŋspoliˌtsaɪ], meaning 'Order Police') were the uniformed police force in Nazi Germany from 1936 to 1945. The Orpo was absorbed into the Nazi monopoly of power after regional police jurisdiction was removed in favour of the central Nazi government ("Reich-ification", Verreichlichung, of the police). In 1936, Heinrich Himmler, the commander (Reichsführer-SS) of the Schutzstaffel (SS), was appointed Chief of the German Police in the Interior Ministry. The top and upper leadership positions of the Orpo were filled by police officers who belonged to or had joined the SS. Owing to their green uniforms, Orpo members were also referred to as Grüne Polizei (Green Police). The force was established as a centralised organisation based in Berlin uniting the municipal, city, and rural uniformed police that had been previously organised on a state-by-state basis.
The Ordnungspolizei encompassed virtually all of Nazi Germany's law-enforcement and emergency response organisations, including fire brigades, coast guard, and civil defence. Himmler and Kurt Daluege, chief of the Orpo, worked to transform the police force into militarised formations ready to serve the regime's aims of conquest and racial annihilation. Police troops were first formed into battalion-sized formations for the invasion of Poland, where they were deployed for security and policing purposes, also taking part in executions and mass deportations. During World War II, the force was tasked with policing the civilian population of the occupied and colonised countries. In 1941, the Orpo's activities escalated to genocide after the Order Police battalions formed into independent regiments or were attached to Wehrmacht security divisions and Einsatzgruppen. Independently and in collaboration with those units, members of the Orpo perpetrated crimes against humanity and mass-murder during the Holocaust.