In order to successfully innovate, the firm will combine different innovation activities. In this paper we show that there exist important complementarities between the different innovation activities. Using data from the Community Innovation Survey on Belgian manufacturing firms, we find that firms that are only engaged in a single innovation strategy, either internal R&D activities or sourcing technology externally, introduced fewer new or substantially improved products compared to firms which combine internal and external sourcing. In the adoption approach we show that the different innovation activities are strongly positively correlated and identify a capacity to strategically protect intellectual property and a more basic R&D base as common drivers, resulting in the perceived complementarity between these innovation activities.