The communication of fashion brands, traditionally focused on product sales, has increasingly taken on an active role in conveying messages aligned with modern values of sustainability and ethics, driven by growing awareness of the textile industry’s social and environmental impacts. In this context, communication is essential in shaping consumers’ perceptions of brands, in sharing brand values, purpose, and practices. Communicating transparency emerges as a fundamental value, as it allows consumers to make more informed decisions and holds brands accountable for their actions. This article analyzes the interrelation between brand communication, sustainability, and transparency in the fashion industry, exploring how brands use online communication to build an image of social and environmental responsibility. Throughout the article, the challenges and opportunities of transparent communication will be addressed, as well as the role of activist organizations and legal regulations in promoting more sustainable and ethical practices in the fashion industry. However, this study does not examine the transparency and accuracy of the information itself but rather analyzes how brands communicate their sustainability messages in a transparent manner. This work is part of a master’s dissertation project and is divided into two parts: a literature review and a comparative case study between Stella McCartney and People Tree, demonstrating the importance of fashion brands’ sustainability transparency on their official websites.