The emergence of cleantech industry offers a unique context to explore and develop entrepreneurship theories. Cleantech ventures are important agents of environmental innovation, they exploit technological knowledge contribute to an increased use of energy from renewable sources or to a more environmentally friendly handling of waste. They represent an extreme case of technology entrepreneurship: combining a strong focus on capital-intensive technologies with complex industrial markets.

Cleantech ventures face greater firm and industry-level legitimacy challenges while accessing external resources, compared to high-tech ventures operating in more established (legitimized) industries. Zimmermann and Zeitz (2002) suggested that achieving a legitimacy threshold is related to the emergence of a new venture. However, from the stage-based theory perspective, gaining legitimacy is associated with overcoming critical junctures (Vohora et al. 2004). Instead of a unique threshold, cleantech ventures might have to build and sustain legitimacy across different stages, overcoming legitimacy thresholds (Fisher et al. 2016). Our study examines how cleantech ventures pursue the process of signaling towards external parties to reach important entrepreneurial milestones in different development stages. We address the following research questions: • Why and how do the cleantech ventures signal to gain legitimacy, and • What signals do they send in the start-up and growth (late) stages?