The cooperation began in the early 1980s with a meeting at a scientific conference and developed rapidly. In the mid-1980s, Professors Kacprzyk and Fedrizzi published an article on a new measure of the degree of consensus in a group of experts, which initiated a new direction of research in the literature. During this period, Professor Sławomir Zadrożny from the Systems Research Institute, Polish Academy of Sciences, and Professor Franco Molinari from the University of Trento joined the team. The research was launched on computerized group decision support and consensus-building systems that have found their application in municipal planning in Italian cities. The group was also joined by Professor Hannu Nurmi from the University of Turku (Finland). This allowed for an intensification of research, including the analysis and comparison of voting methods. An important result of this cooperation was the organization of the joint Polish-Italian, and then Polish-Italian-Finnish conferences, under the auspices of the Polish Academy of Sciences, alternately in these countries. This fruitful scientific cooperation of Polish scientists, Professors Janusz Kacprzyk and Sławomir Zadrożny, with the Italian and Finish partners, Professors Mario Fedrizzi, and Hannu Nurmi, is constantly developing, which has resulted in over 50 joint scientific papers, many of which appeared in prestigious journals and conference materials.