This paper examines the link between firm size and innovation. Given that innovation is highly reliant on human capital, the ability to attract, motivate, and retain high quality inventors is a key determinant of firm innovation. Firm size may affect these abilities, and small firms are known to account for a disproportionate share of aggregate innovation. I therefore investigate the role that sorting of inventors across firms plays in explaining this disparity. Talented inventors may find employment at a large firm less attractive due to the relative absence of growth options and a lower ability to link compensation to performance. Using inventor-level patent data, I construct employment histories for inventors at U.S. public firms. I find that the most productive inventors are disproportionately likely to move to small firms, while the least productive inventors disproportionately remain at large firms. These results cannot be explained fully by small firms' superior growth opportunities. In addition, productive innovators' turnover in small firms is sensitive to the level of option compensation. Taken together, this evidence is consistent with inventor sorting explaining part of the firm size innovation gap.