Every human activity requires a space—and work is no exception. Although ergonomists investigate the design of workspaces, the notion of space itself remains poorly conceptualized; despite the fact that ergonomics recognizes that space is an important part of a work situation. This paper examines the concept of space in the workplace. Specifically, it focuses on the role of space, and its relationship with work activity.The concept of space has multiple meanings, while the concept of the workplace is equally imprecise. The word ‘space’ is abstract, which raises the question of its historical and theoretical roots. Our approach considers space as both an instrument, and as emerging from activity: the aim is to characterize the relationship between space and activity. This empirical field study examines the activity of sorting post. The concept of the space of activity is proposed, which draws upon two theoretical frameworks. The first refers to the instrumental approach that is found in ergonomics, and shows how a given space (as an artefact, an object or an environment) is changed by, and during, the activity of workers. The second relates to the enaction approach. The aim here is to capture the dimension of space that emerges during activity. The space of activity is constructed simultaneously by work activity and space. From an ethnomethodological perspective, it is a local production. Space and activity continuously interact in a process of mutual transformation.These two frameworks offer a way to examine the complex, multifaceted concept of the space of activity. Each suggests a way to think about space more clearly, and encourages the consideration of the spatial dimension in work analyses. The latter represents a new unit of analysis that can take into account the characteristics of the spatial dimension in the workplace.