'Wieniec' was a Polish undertaking by the Związek Odwetu (union of retaliation, a resistance organisation concentrating on sabotage) against German rail transport within Poland (7/8 October 1942).

The operation targeted the infrastructure of the Polish railway network near Warsaw. Operations of a similar nature, aimed at the disruption of the German transport and communications network in occupied Poland, continued into the middle part of of 1944, and targeted railroads, bridges and supply depots, primarily near transport hubs such as Warsaw and Lublin.

The Związek Odwetu was created on 20 April 1940 by Major General Stefan Paweł Rowecki, head of the Związek Walki Zbrojnej (union of armed struggle), as the branch of that organisation concentrating on sabotage and diversion. The Związek Odwetu was created out of a number of existing sabotage groups, which were then merged into the ZWZ but later separated once more to reduce the chance of the entire ZWZ being destroyed through any German penetration of one of its sabotage cells.

Initially led by Major Franciszek Niepokólczycki Teodor, the Związek Odwetu was focused on the reduction of German military and industrial potential through active and passive sabotage. It also carried out a number of revenge actions as a reprisal for particularly brutal German mass shootings, summary seizures and other actions targeted on Polish civilians. The net of sabotage and intelligence cells organised by the Związek Odwetu included almost every major German-controlled factory in occupied Poland, as well as a number of special detachments for use by the headquarters of the Związek Odwetu for especially difficult actions.

In February 1942, Generał broni Władysław Eugeniusz Sikorsky, the commander of the Free Polish forces and the prime minister of the Polish government-in-exile, withdrew his order that only limited armed resistance should be made to the German forces in Poland, and the network operated by the Związek Odwetu started to grow significantly as it organised a number of high-profile actions against the German war effort. Out of these several hundred thousand actions, undertaken primarily in Silesia, Lesser Poland, the Holy Cross Mountains and Mazovia, perhaps the best known is 'Wieniec'. In this, the Związek Odwetu blew up all the rail lines into and out of Warsaw, destroyed four German supply trains heading toward the Eastern Front, and disrupted the movement of all supplies for several days.

During December, this effort was continued by the Związek Odwetu in eastern Poland as a reprisal for German terror operations in the area around Zamość.

After the ZWZ had been re-formed into the Armia Krajowa, the Związek Odwetu was once again incorporated into it, merged with the Wachlarz (formed by the Armia Krajowa for sabotage duties behind the German lines on the Eastern Front outside the border with Poland) and other such units, and as such formed the backbone of the Kedyw active and passive sabotage organisation within the Armia Krajowa.

During the later stages of its existence, the Związek Odwetu was headed by Major Jan Wojciech Kiwerski. Rowecki was the cmmander-in-chief of the Armia Krajowa in 1943/44 until seized by the Germans, sent to Sachsenhausen concentration camp and then executed.