The growing attention to sustainability and circular economy has made the fashion industry one of the most discussed sectors in terms of environmental and social impact. The second-hand fashion industry emerges as an innovative response to the inefficiencies of fast fashion, promoting waste reduction, extending product lifecycles, and material circularity. This research explores the innovative business models adopted by start-ups in the second-hand fashion sector, aiming to understand how these companies contribute to sustainability goals by integrating economic, environmental, and social aspects. The sample analyzed includes 11 start-ups, selected for their ability to innovate within the circular fashion context, using qualitative methods based on interviews and analysis of their digital platforms.