This paper will explore how the often illegal activities of hackers (employed in the original usage of the term to refer to individuals who modify computer hardware and software) may produce valuable innovations. The paper argues that structural changes, including a growth in the number of knowledge workers, has resulted in a burgeoning community of users able to modify or hack existing products, or develop products that compete with existing suppliers. The paper will introduce the complementary concepts of Outlaw Innovation and the Outlaw User, locating them within the literature on users. The paper will explore how firms react to this activity and provide case studies of this phenomenon. The paper will argue that Outlaw Innovation represents an extension in our understanding of the way in which firms interact with users, presents a series of policy challenges, and opens a promising area for further research. A series of possible research questions will be outlined and the paper will conclude by indicating the next steps in the development of this line of enquiry.