Until seven years ago, user innovation studies focused on specific cases or industries, leaving room for criticism that the phenomenon is marginal. This chapter summarizes and discusses the empirical work concerned with the scope of user innovation in broader samples. A first finding is that user innovation is widespread. The share of firms developing and/or modifying processes for in-house use is generally about 15 to 20 percent, while amongst consumers four to six percent innovated to satisfy personal needs in the past three years. This corresponds with millions of innovating businesses and consumers across the globe. For firms, user innovation indicators measure process-related innovation activities which remain partly invisible in official surveys, while user innovation by individual consumers is not at all present in the official statistics. A second finding is that user innovation is more open than traditional, producer-oriented innovation. Especially innovating consumers do not patent their knowledge, and 10 to 30 percent of them even shares their knowledge freely with other users and/or adopting businesses. Finally, it appears that users’ innovations can be useful to other economic actors. Diffusion mechanisms include free revealing to other users, new venture creation, and adoption by commercial producers. Overall, the empirical studies suggest that user innovation indicators should be part of the official innovation metrics.