The Self-Defence of the Republic of Poland (Polish: Samoobrona Rzeczpospolitej Polskiej, SRP) is a Christian socialist, populist, agrarian, and nationalist political party and trade union in Poland. The party promotes agrarian socialist and Catholic socialist economic policies combined with a left-wing populist, anti-globalization and anti-neoliberal rhetoric. The party describes itself as left-wing, although it stresses that it belongs to the "patriotic left" and follows Catholic social teaching. The party is sympathetic to Communist Poland, which led political scientists to label the party as neocommunist, post-communist, and far-left.

Though considered a "political chameleon", Self-Defence of the Republic of Poland is generally regarded as a left-wing party by historians and political scientists. According to Andrzej Antoszewski, Self-Defence was a radical left-wing party that by postulating the need to stop privatisation and protect workers' interests, often overlapped with neo-communist parties. In English-language literature, the party is described as a radical left-populist party. In the wake of the SLD's electoral defeat in 2005, Self-Defence was sometimes referred to as the "new left". It was also called a left-wing party with a populist-agrarian face. Political scientists also described it as socialist, allowing it to form alliances with the Democratic Left Alliance. On the other hand, its anti-neoliberal and nationalist narrative also allowed it to briefly cooperate with PiS and LPR in 2005.

Founded by Andrzej Lepper in 1992, the party initially fared poorly, failing to enter the Sejm. However, it was catapulted to prominence in the 2001 parliamentary election, winning 53 seats, after which it gave confidence and supply to the Democratic Left Alliance government. It elected six MEPs at the 2004 European election, with five joining the Union for Europe of the Nations and one joining the PES Group.

It switched its support to Law and Justice (PiS) after the 2005 election, in which it won 56 seats in the Sejm and three in the Senate. Lepper was appointed Deputy Prime Minister in the coalition government with PiS and the League of Polish Families. In 2007, he was dismissed from his position and the party withdrew from the coalition. This precipitated a new election, at which the party collapsed to just 1.5% of the vote: losing all its seats. On August 5, 2011, the Party's leader, Andrzej Lepper, was found dead in his party's office in Warsaw. His death was ruled a suicide by hanging.

The origins of Samoobrona date back to a spontaneous protest movement of farmers from Western Pomerania (the Darlowo area is the hometown of A. Lepper) and the Zamojszczyzna region, which developed into a trade union. The very creation of the political party was originally aimed solely at supporting the 'Samoobrona' Trade Union of Agriculture (ZZR 'Samoobrona'), which had played a leading role for a long time. Samoobrona as a movement had communist origins, and it originally was a peasant movement associated with the Polish People's Party, which back then was an agrarian socialist party associated with the fallen communist regime, and was considered one of the post-communist successor parties based on the nostalgia for the previous, socialist regime.

As Lepper reported many years later. Lepper, the idea to create a trade union, and then a political movement, was born after a meeting with Deputy Prime Minister Leszek Balcerowicz in the autumn of 1991: "Everything that happened afterwards - with me and Samoobrona - I therefore owe, to some extent, to that two hours long conversation of 10 years ago". In January 1992, the Trade Union of Agriculture "Samoobrona" was registered. The political party, which initially appeared under the name Przymierze "Samoobrona", was registered on 12 June 1992. In addition to representatives of ZZR "Samoobrona", it also included activists from the Metalworkers' Trade Union and a Green faction headed by J. Bryczkowski. In its first political declaration, Samoobrona described itself as a "radical" party that represents the interests of the economically disadvantaged and those living in poverty.

The beginnings of party's activities date to Lepper's home village Darłowo, which has been plunged into poverty between 1989 and 1991 as a result of the neoliberal Balcerowicz Plan, which dismantled the socialist economy in Poland in favor of a capitalist free-market one. As the state sector of agricultures was dismantled and privatized, rural areas experienced an extreme spike of unemployment, poverty and social exclusion. Unfavourable prices of agricultural products on the market further aggravated the situation - between 1990 and 1991, agricultural prices increased threefold while industrial prices increased tenfold, drastically diminishing the purchasing power of Polish agriculture. This was combined with a huge decrease in farmers' real income. In Lepper's region, the situation became particularly critical as a result of heavy rainfall, which caused local flooding.

On 18 January 1991, the first rally was organised in Darłowo, attended by local farmers and the unemployed, including Andrzej Lepper. During the rally, protesters formed the Self-Defence of the Unemployed Homeless Association of the Pomeranian Region Darłowo (Polish: Stowarzyszenie Samoobrona Bezrobotnych Bezdomnych Regionu Pomorskiego Darłowo). Samoobrona itself was then founded on 27 July 1991 as a trade union Protest Committee of Self-Defence of Farmers (Polish: Komitet Protestacyjny Samoobrony Rolników), with Lepper being elected as its leader. First protest initiated by Lepper then took place on 5 August 1991, which demanded that the state of natural disaster be declared in Darłowo, along with demanding special aid and compensation to affected farmers. Lepper also made an appeal to the local voivode that the government temporarily suspends the enforcement of unpaid debts on local citizens. His plea was ignored.