The global clothing and footwear industry accounted for only 2 percent of the world’s Gross Domestic Product (Strijbos, 2016), but disproportionately contributed "… between 5 and 10% of global pollution impacts in 2016" (Quantis, 2018, p. 18). This industry has also been criticized for exploitative labor practices. When surveyed, consumers have reported preferences for environmentally and socially responsible clothing, yet they have continued to seek low-cost, low-quality clothing that belies their good intentions. Among sustainable clothing scholarship and activism there has been broad, but untested consensus that increasing consumer knowledge among the general population about sustainable clothing will promote sustainable clothing consumption. Academics, activists, and concerned social entrepreneurs have spent their efforts creating a variety of online sustainable clothing consumer knowledge resources without empirical proof that consumer knowledge influences consumer behavior, and there are no best practices that have been established. The purpose of this study was to evaluate the efficacy of one online sustainable clothing consumer knowledge platform, ProjectJUST.com, in promoting sustainable clothing consumption among Millennials. Quantitative survey results and qualitative interview findings were analyzed to this end. Survey results collected from two groups of respondents, one that had used ProjectJUST.com (n = 700) and one that had not (n = 685). Survey results suggested that people who accessed ProjectJUST.com already intended to buy sustainable clothing when they landed on the website because the content was personally relevant to their expressions of identity as more sustainable consumers. Qualitative data were derived from 3 interviews spaced over 6-months with 35 Millennials. Findings suggested that ProjectJUST.com had little appeal for this study’s participants. Participants preferred to receive information about their clothing from sources that they already used, such as social media, or word-of-mouth. Participants were then segmented based on the changes they reported to their clothing consumption behaviors over the study period into four groups: maintainers, preparers, contemplators, and precontemplators. Differentiated social marketing strategies were recommended, and implications for online sustainable clothing consumer knowledge platforms were presented throughout to offer strategies that can improve the efficacy of such platforms in changing behavior.