This Open Debate addresses the theme of missing data as a field of investigation for design, and as an opportunity to rethink the relationship between knowledge, technology and representation. In contemporary digital systems, the production and circulation of data define what is recognised, stored and remembered. In this scenario, design takes on a critical role in questioning the logic with which data is collected, ordered and made visible. The aim of this issue is to understand how design can intervene when the information is missing or partial, transforming such gaps into tools for reflection and experimentation.