Innovation is the core element of economic growth and sustainable development. While there is emerging literature showing that cooperation is a vector of innovation, very little is known in the context of developing countries and particularly in the context of Cameroon, were there is existing enormous potentiality of innovation and economic growth. Therefore, this study aims to evaluate the effect of cooperation on firms' capacity to innovation. The empirical analysis focuses on the unobserved heterogeneity of externalities. The data analysis is based on a sample of 640 companies. The estimation method is a probit with selection from the analytical framework proposed by Heckman in 1979. The estimation is performed in two steps using the maximum likelihood estimator. The results revealed the existence of unobserved elements, due to cooperation, that reinforce the innovation capacity of firms. More specifically, the findings seem to suggest that the social benefits of R&D outweigh the private benefits, which is in line with external studies. To this end, innovation promotion policies should be oriented towards the promotion or intensification of cooperation in innovation. Future studies must take this into account