Patent trolls—firms that appropriate profits from innovation by enforcing patents against infringers—are peculiar players on markets for technologies. As buyers of patents, they are solely interested in the exclusion right, not in the underlying knowledge. Similarly, when they sell or license out patents, the transaction does not involve a technology transfer. In this paper, we empirically analyze trolls ’ patent acquisitions. We draw on a unique dataset of 753 patents acquired by known patent trolls, which we compare to 1506 patents acquired by practicing firms. Our findings regarding patent characteristics support recent theoretical propositions about the troll business model. Trolls focus on patents that have a broad scope and that lie in patent thickets. Furthermore, and contrary to common belief, we find that troll patents are of significantly higher quality than those in the control group, a result that suggests sustainability of the troll business in the future. Extrapolating from our findings, we posit that transactions involving patent trolls may only be the tip of the iceberg of “patent-only ” transactions, a conjecture with strong implications for the efficiency of markets for technologies. Managerial and policy implications are discussed.