In this paper, the suppliers’ contributions to their customers’ processes are analysed from the perspective of the supplier, and the conditions for mutual learning are discussed. The study is based on case studies of six suppliers connected to three lift truck companies. The case studies reveal that collaboration is not fully developed, and the reasons for this are analysed. The barriers to mutual learning seem to relate to the customers’ demands for price reductions, the customers’ lack of interest in co-operating, unequal relations between customer and supplier, and constraints regarding co-operation with the customers’ competitors.