This paper highlights the distinction between knowledge-intensive firms and patent trolls. Both are "fabless" firms since they have no manufacturing capacity. However, they follow very different logics of patent utilization. The emergence of firms specialized in knowledge production is a pillar of the knowledge-based economy. Knowledge -intensive firms use the patent system to prevent infringement and to valorize their important R&D investments in the technology market. In contrast, patent trolls are looking for infringements. They abuse the patent system and use the complexity and uncertainty associated with patent litigation in order to extort money from innovators. Their social value is at best uncertain, at worst fully negative. The paper concludes by proposing policy measures that could reduce the trolling phenomenon while not deterring the emergence of intensive new -knowledge intensive actors. JEL codes: D2, O3