There is an extensive theoretical and empirical discussion regarding the linear relationship between R&D expenditure and innovation. However, the innovationdecision is not dichotomous since it implies the choice of a combination of technological and non-technological innovation options. Similarly, not only does internal R&D spending allow firms to innovate, but so-called non-R&D activities also allow firms to develop innovations. In this thesis we analyze two theoretical currents found in the innovation literature, innovation strategy and innovation complementarity, to discuss and show which of them allows us to better explain the innovation-decision of firms. We also analyze the effect that internal and external characteristics of firms have on their preferences for the types of R&D and non-R&D activities for the development of innovations