The article presents the results of a comparative historical analysis of the foreign policy sections of the programs of the Czech Social Democratic Party and the Communist Party of Bohemia and Moravia using documents from their current archives. Particular attention in the approaches of the two parties is paid to the issues of the integration of the Czech Republic into the structures of NATO and the European Union. Based on the study of the available scientific literature, a conclusion is made about the need to consider this problem through the prism of two main lines in the context of European integration: security policy and economic rapprochement with the EU. Fundamental differences in the interpretations of Czech Social Democrats and Communists about the prospects for their country's entry into European and Euro-Atlantic associations have been revealed. If the Social Democrats defended the need to “enter Europe” and even into its “core”, seeing this as a significant benefit for the country’s economy due to the free movement of labor, protection from currency crises and a reduction in transaction costs, the Communists called for maintaining the focus on a multi-vector foreign policy of the state – cooperation with all countries of interest to the Czech Republic. At the same time, both parties, although with varying degrees of intensity, resorted to criticism of European institutions. The results of the study help to identify the reason why the major Czech left-wing parties lost the elections to the lower house of the Czech Parliament in 2021.