This paper aims to trace down the origins of radical inventions. In spite of many theoretical discussions on the effect of radical inventions, the specific nature of radical inventions has received much less attention in the theoretical and empirical literature. We try to fill that void by an empirical investigation into the specific origins of radical inventions. We explore this issue by a close examination of 157 individual patents, which are selected from a pool of more than 300,000 patents. In contrast to the conventional wisdom that radical inventions are based less on existing knowledge, we find that they are to a higher degree based on existing knowledge than non-radical inventions. A further result that follows from our analysis is that radical inventions are induced by the recombination over more knowledge domains. The combination of knowledge from domains that might usually not be connected seems to deliver more radical inventions.