Sustainability entrepreneurs act based on expectations about how products will be received by consumers, in which directions markets and demand will develop, or which business models and innovations will prevail. Through their action-guiding function, expectations play an important role in how sustainability ventures develop in and out of niches. However, little attention has been paid to how new communication media, especially increasingly important social media, affect the way entrepreneurs articulate and change their expectations. This paper addresses this research gap using transformative learning theory to examine the communication of Mexican sustainable fashion entrepreneurs on Instagram. We used snowball sampling to select a representative sample of fashion brands operating in the sustainable fashion niche in Mexico. We used a mixed-methods approach: To analyze entrepreneurs' expectations, their use of social media and other learning outcomes, we employed semi-structured interviews. To track the evolution of entrepreneurs' expectations and their activity on Instagram, we scraped content (posts) from their respective brands' pages. Fashion brands in Mexico with business models based on sustainable fashion are a mixture of market-based and grassroots initiatives. Although sustainability concerns drive the ventures of sustainability entrepreneurs, Instagramhas played a crucial role in the evolution of entrepreneurs' expectations towards innovation with products and business growth. This change in expectations can be understood as a transformative learning process that underscores different phases, action engagement, disorienting dilemmas and discourse. We contribute to opening and exploring the black box regarding the learning processes in the articulation and evolution of expectations.