Decisions on co-operating and with whom are the first topics considered by firms when they begin a joint investigation project. This work studies both problems using a sample of 1653 Spanish industrial firms. The results suggest that in Spain firms cooperate to correct their deficiencies when innovating. However, questions related to the market are of limited importance and large sized firms resort more to cooperation. We find that in order to undertake cooperative R&D it is necessary to have certain internal capacities in this area. We also show that cooperation with customers and suppliers is more common than cooperation with competitors. Furthermore, the three types of partners are chosen for different reasons. Firms that belong to sectors with a lower technological intensity and that acquire technology tend to cooperate with their suppliers to improve the quality of their products and their national market share. On the other hand, firms that belong to sectors with a higher technological intensity have a greater propensity to cooperate with their customers to substitute their current products. Both types of cooperation are carried out with Spanish and international firms. However, cooperation with competitors has an international character and is carried out within the context of international programs of innovation.

Key words: R&D cooperation, vertical cooperation, horizontal cooperation.
JEL classification: D74, L20, O34.