To address today’s sustainability challenges a shift is needed in the way products are designed. The behavior of design practitioners plays an important role in this as 80% of a product’s environmental impact is determined during the design phase. The Fogg Behavior Model (FBM) shows that three elements (Motivation, Ability and Trigger) are needed for behavioral change. When applying this to Design for Sustainability (D4S), the consideration and harmonization of ecological, economic and social aspects in the design process, which includes Product Lifetime Extension, multiple barriers and enablers that influence FBM, could be identified. This study aims at mapping these in the context of Flemish design agencies. The goal is thus to identify the barriers and enablers designers in Flemish design agencies face when applying D4S and how these affect the behavior of these practitioners. For this, multiple (n=9) semi-structured interviews have been performed and analyzed using an adapted approach, this to challenge the preconceived hypotheses. Results show that multiple aspects influence the designer’s behavior. These aspects can be subdivided into four main external categories, Design agency, Client requests and constraints, Government and Non-customized tools. It is unclear what the personal motivation of design practitioners is to apply D4S, but limited knowledge on this subject hinders them in doing so. The researchers hope to contribute to the D4S research field and make its application standard practice. ; info:eu-repo/semantics/published