This special issue of Journal of Writing Research addresses the fundamental question of performance units in writing: how can we characterize these units and which theoretical paradigms allow us to describe them? Despite their core role in the writing activity, there is no consensus on the nature of written performance units. In order to progress on this issue, the different articles presented in this special issue shed light on performance units, their description, definition and role in text construction. Different methodological and theoretical approaches, based on behavioral data, with pauses as a central indicator, illustrate how linguistic structures produced in these units constrain written production.