This chapter documents instances from past centuries where inventors freely shared knowledge of their innovations with other inventors. It is widely believed that such knowledge sharing is a recent development, as in Open Source Software. Our survey shows, instead, that innovators have long practiced collective invention at times, including in such key technologies as steam engines, iron, steel, and textiles. Generally, innovator behavior was substantially richer than the heroic portrayal often found in textbooks and museums. Knowledge sharing sometimes coexisted with patenting, at other times, not, suggesting the importance of policy that accommodates knowledge sharing to foster cumulative innovation.