This paper investigates the effects that knowledge sources external to the firm have on its environmental innovations (EIs). Using the CIS 2006-2008, we refer to both the probability to introduce an EI and the number of EI-typologies adopted by firms. We estimate the impact of the “depth” and “breadth” of knowledge sourcing. In addition, we test for the moderating role of the firm's absorptive capacity. In general, knowledge sourcing has a positive impact on both types of EI-performance. However, a broad sourcing strategy reveals a threshold, over which the propensity to introduce an EI diminishes. Cognitive constraints in processing knowledge inputs that are too diverse could explain this result. Absorptive capacity generally helps firms in turning broadly sourced external knowledge into EI. Conversely, internal innovation capabilities and knowledge socialization mechanisms seem to diminish the EI impact of knowledge sourced through intense external interactions. The possibility of mismatches between internal and external knowledge and problems in distributing the decision-makers’ attention between the two could explain this result.