This chapter highlights the importance of sustainability for consumers, within the scope of co-creation, in fashion design. In the field of sustainability, it is therefore necessary to understand which of its aspects are most important to the consumer. The methodology of the chapter is based on two methods that complement each other. Based on a qualitative methodology, the first method focuses on the contextualization of the theme through the reading and analysis of books, scientific articles, theses, and reports in the scope of sustainability and co-creation in fashion design. The second method of a quantitative nature focuses on the analysis of data from a questionnaire to a sample of 404 participants from Portugal. The results indicate that knowing that the brand does not have social ethics is the most important aspect for the consumers in co-creation brands when regarding sustainability. However, consumers also pointed out that not knowing where or how the product was produced and knowing that the brand and its products are not sustainable are also of importance to them. This chapter makes it clear that consumers who co-create or would like to co-create fashion products are effectively interested in co-creation brands being sustainable in various aspects of their business.