The Milicja Obywatelska (Polish pronunciation: [miˈlit͡sja ɔbɨvaˈtɛlska]; MO), known as the Citizens' Militia in English, was the national police organization of the Polish People's Republic.

The MO was established on 7 October 1944 by the Polish Committee of National Liberation under Chief Commander Franciszek Jóźwiak to police Red Army controlled areas of Poland during World War II. It became the official police force with the founding of the Polish People's Republic in 1947, effectively replacing the pre-war Policja as the main uniformed civilian police of Poland during the communist era. The MO was headquartered in Warsaw while training for the force was conducted in the town of Legionowo.

The MO was supported by two paramilitary formations: the elite Motorized Reserves of the Citizens' Militia (ZOMO) and the reservist Volunteer Reserve of the Citizens' Militia (ORMO). In most cases it represented a state-controlled force used to exert political repression, especially with its elite ZOMO squads. The MO continued to exist after the fall of communism in Poland in 1989 until it was transformed back into Policja on 10 May 1990.

The Citizens' Militia (MO) was created on the basis of provisions of the July Manifesto of the Soviet-backed Polish National Liberation Committee (PKWN), State National Council. It was formally established by decree on 7 October 1944 during the later stages of the Eastern Front of World War II. Milicja had been adapted from the cognate term militsiya used in the Soviet Union, itself derived from militia with its etymology from the concept of a military force composed of ordinary citizens.

The MO was used to establish the authority of the PKWN in areas of Poland that came under control of the Red Army as it pushed through the country into Nazi Germany. The first generation officers and agents were drawn from the following groups and sectors of society:

Poland came under the domination of the Soviet Union at the end of World War II and, following the rigged 1947 Polish parliamentary election, the PKWN-derived Provisional Government of National Unity was able to legitimise itself enough to supplant the London-based Polish government-in-exile recognized by the Western allies. The MO effectively became the official civilian police force of Poland replacing the Policja. Former members of the anti-communist underground such as the Home Army, who tried to ensure an influence on everyday life, joined the new force, to the point that the entire outposts were Home Army members. The MO was supplemented by about a thousand former policemen employed in 1945, mainly in positions requiring special qualifications.

In 1948, Poland's strengthened turn toward Stalinism brought the beginning of formalised totalitarian rule, "in which one Party ruled autonomously over all sections of society". Officers of the MO took the same solemn oath as the officers of the Security Service. Its main fragment read as follows:

I solemnly vow ...- to faithfully serve the Fatherland, the Party and People's Authority and to protect the law, order and public safety.