In this chapter, the system of knowledge mobilized in architects’ work is examined. Since the work of the site manager considered in the previous chapter is rather different from the work assignments facing the practising architect, this chapter uses a complementary theoretical framework to address the skills and capabilities involved in architects’ work. In the discussion of this work, a distinction is made between an internal and an external perspective. The internal perspective emphasizes the day-to-day communication among peers centred on models, images, blueprints and other artefacts serving as boundary-objects in architectural work. The external perspective will point at the value of credit and reputation in the field of architecture outside of the focal firm. Architects essentially pursue, similar to many other professional groups and in the performing arts, what has been called ‘portfolio careers’. That is, the entire career trajectory of a practising architect may be laid out as a series of concurrent or succeeding projects that collectively constitute an individual’s career. Every architect can tell stories of what projects they participated in and what competitions they have joined or may even have won; their working life is, just like in the other fields of the construction industry, essentially ‘projectified’. In the analysis of the internal work processes, architects’ work will be examined in analogy with scientific laboratory work. The relative lack of detailed studies such as ethnographies of architectural practice and the abundance of similar studies of laboratory research motivates such a comparative study. Studies in science and technology have traditionally provided a great number of highly detailed ethnographies that are arguably helpful when understanding what architects do in their day-to-day work life and when examining what sources of knowledge they use in their professions. Expressed differently, there is a certain morphology shared between professions notwithstanding their idiosyncrasies and specializations.