This feature issue of the European Journal of Operational Research presents the results of an international comparative study in the development of decision support systems. The study was held in the period 1987–1990 and coordinated by the International Institute for Applied Systems Analysis in Laxenburg, Austria. Teams from Budapest, Cracow/Warsaw, Eindhoven, Genoa, Poznan, Udine/Brescia and Wroclaw developed decision support systems for a resource constrained project scheduling problem; a team from Moscow investigated some structural properties of the problem. Although not all of the goals of the study were fully realized, the study was generally viewed as a worthwhile effort. The reports by seven teams are collected here. Section 1 of this editorial describes the history and goals of the study. In Section 2 we sketch the problem type in question and discuss the functional aspects of a decision support system for operational planning. We evaluate the study in Section 3 and give some conclusions in Section 4.