R&D cooperation is a key to combining firms' internal and external technological capabilities. This article empirically investigates the effect of R&D cooperation partners on different types of product innovation. This study considers four types of partners in R&D cooperation: suppliers, customers, competitors, and universities. Three purposes of product innovation are considered: diversification of products, pioneering a new market, and standardization of technology. The main findings are: (1) R&D cooperation with suppliers and competitors has a positive effect on standardization of technology, (2) R&D cooperation with customers has a positive effect on diversification of products and pioneering a new market, and (3) R&D cooperation with universities has a positive effect on pioneering a new market and standardization of technology.