The purpose of the study is partly to investigate and identify the functions of the professional roles in architecture; architect, landscape architect, plan- or planning architect and interior architect fill in the agencies' external sustainability work such as projects, and partly how the architectural firms' organizational structures are affected by their external sustainability work. Through a qualitative method and semi-structured interviews with five architectural firms, the study wants to create a greater understanding of architectural firms' external sustainability work by examining what their external sustainability work looks like, how the business generates and ensures sustainable results and what functions the different professional roles in architecture play for external sustainability work. The empirical result is analyzed using previous research and published theories and results in the conclusion that three of the four architectural roles, architect, landscape architect and1interior architect, contribute to the architectural firms' external sustainability work with the help of education, experience, knowledge and competence. One of the four professional roles, plan- or planning architect, is not employed at any of the architectural firms examined and the study can thus not determine what function the professional role plays in the external sustainability work. The study also shows that the architectural firms' external sustainability work affects their organizational structures, as the design and structuring of the architectural firms largely depends on what the projects look like. All surveyed architectural firms are project-based and adapt their teams and structures to what the projects require.