Why do some inventors build up knowledge in a broad variety of technological areas, while others stick to their field of expertise? Recent research has shown that inventor teams involving an individual with diverse knowledge are more likely to introduce breakthrough inventions. In the light of a general trend towards specialization and teamwork, this finding raises concern about an undersupply of breakthrough inventions and warrants policy intervention to stimulate individual knowledge diversity. However, to design effective policy instruments, we need to know how highly skilled knowledge workers make decisions regarding the scope of their expertise throughout their careers. To this end, the proposed research aims to explicate the mechanisms driving knowledge diversity decisions of individual inventors.