Design is increasingly present in transdisciplinary sustainability research, yet its role often remains insufficiently theorised and is frequently reduced to methods, facilitation, or communication. This book chapter argues that design should instead be understood as an epistemic and responsibility-making practice that actively shapes how knowledge, participation, time, and transformation are configured.

Bringing together perspectives from transdisciplinary research, design studies, and emerging debates on more-than-human and relational design, the chapter develops a conceptual framework that maps different roles of design, from auxiliary service and methodified toolkit to knowledge-producing and relational epistemic practice. Building on this framework, the chapter introduces a design beyond the human orientation that broadens questions of responsibility beyond individual users and project outcomes to include ecological systems, infrastructures, inherited histories, present conditions, and future consequences.

The chapter concludes by discussing implications for co-creation, knowledge integration, evaluation, and sustainability transformations, positioning design as a critical practice for co-creating new narratives and forms of responsibility under planetary conditions.