This paper provides empirical evidence on the link between different external knowledge-sourcing strategies and firms’ innovation output measured by the number of patent applications. In our analysis, we consider three strategies for acquiring external knowledge (i.e. buying, cooperating and contracting out) and four sources of external knowledge acquisition (i.e. industrial firms, universities, technical colleges and public research institutions – each either domestic or foreign sources). The analysis is based on a sample of 970 Austrian firms in 2008. Using zero-inflated count data models, we find that sourcing from higher education and public research organizations is significantly positively related to innovation output in general, while sourcing from other firms is only weakly significant. Among the different strategies buying and cooperating from/with higher education and public research institutes have a higher impact on the number of patent applications as compared to contracting out. Furthermore, universities as the source of knowledge have a significant impact, while technical colleges and public research institutions are not significant. Finally, domestic sources are at least and (in some cases) more powerful in determining the number of patents as compared to knowledge sources from abroad.