A major resource of technological innovativeness is knowledge, which can be either internally or externally derived, and constrained or abundant. We employ a longitudinal case study of U.S. industries to assess whether knowledge sources—internal or external to a country's domestic technology—affect an industry's technological innovativeness, and whether knowledge constraints affect technological innovativeness. We use more than 175,000 U.S. patents over 16 years. In contrast to the prevalent thinking that resource constraints inhibit innovation, we find trade-related knowledge constraints are largely positively associated with the innovativeness of technological output. Moreover, although one may expect a negative relationship between internally derived knowledge based on prior technology and technological innovativeness, we find this relationship is curvilinear.