This paper analyzes how incumbent firms act to shape markets for new technology alternatives. It introduces a framework that highlights important linkages between the dynamic market-shaping capabilities of individual firms and market-shaping processes on a system level. The framework is used to analyze the endeavors of two large heavy vehicle manufacturers to introduce two technology platforms—electrified trucks and trucks fueled by liquefied gas—as alternatives to traditional diesel-fueled trucks. The analysis shows how incumbent firms deploy market-shaping capabilities to claim legitimate positions in envisioned future markets. The paper concludes by pointing to the dynamism of market interactions in sustainability transitions, showing how firms induce system-level reconfigurations and how such reconfigurations induce changes at the level of the firm. © 2021 The Author(s)