This document provides an introduction to transdisciplinary research from the Network for Transdisciplinary Research (td-net). It defines transdisciplinary research as aiming to solve societal problems through close interaction with stakeholders. The research process links scientific knowledge production with societal problem solving through co-production of knowledge. Principles of transdisciplinary research include grasping complexity, considering diverse perspectives, linking different types of knowledge, and promoting the common good. Stakeholder participation and collaboration across disciplines are key to applying these principles.