We explore heterogeneities in the determinants of innovating firms' decisions to engage in r&d cooperation, differentiating between four types of cooperation partners: competitors, suppliers, customers, and universities and research institutes (institutional cooperation). We use two matched waves of the dutch community innovation survey (in 1996 and 1998) and apply system probit estimation. We find that determinants of r&d cooperation differ significantly across cooperation types. The positive impact of firm size, r&d intensity, and incoming source-specific spillovers is weaker for competitor cooperation, reflecting greater appropriability concerns. Institutional spillovers are more generic in nature and positively impact all cooperation types. The results appear robust to potential simultaneity bias.