The paper has presented basic issues and directions of operational work carried out by the Second Department (in charge of counterintelligence) of the Provincial Headquarters of the Civic Militia from 1956 to 1964 in relation to discovering, fighting and preventing the crime of espionage. Counteracting espionage carried out by foreign states has always been a key task of each counterintelligence service. In Poland, however, until the mid-1950s, the charge of espionage was used mainly to eliminate political opponents. The situation changed in the period between December 1954 (liquidation of the Ministry of Public Safety) and November 1956 (inclusion of special services into the structures of the Ministry of Internal Affairs). The basic reason for it – following transformation of the Polish October of 1956 – was radical rationalization of the judicial decisions by the Supreme Military Court in relation to Art. 83 (previously bearing number 90) of the Criminal Court of the Polish Army from 23 Sep. 1944, as well as Art. 7 of the decree on crimes especially dangerous in the period of reconstruction of the State from 13 June 1946 (the so-called petty criminal code). The process was, of course, inspired top-down by the communist party authorities, however – luckily – it tuned out to be not a tactical change, but a permanent trend. The essential source bases were files collected in the Branch Office for Preservation and Dissemination of Archival Records at the Institute of National Remembrance in Rzeszów. The Author has also used similar documents kept in the Warsaw headquarters of the OP&DAR at the INR, as well as intradepartmental publications.