Our world is in a state of critical transition demanding new, creative, ecosystemically fit and sustainable responses to complex challenges. We need both new types of knowledge and new modes of knowledge production. Interdisciplinarity and Transdisciplinarity have the potential to support more congruently complex forms of knowledge (differentiated, integrated, recursive, emergent, ecosystemically fit). Their success is dependent on a deeper understanding of their own organizational complexity. In this paper, I highlight key knowledge gaps and research questions for the development of a richer knowledge base to guide the intentional management and facilitation of Interdisciplinarity and Transdisciplinary Relations toward creative and abductive outcomes. I defend the investigation of creativity and abduction, as hallmarks of the complexity of Interdisciplinarity and Transdisciplinarity, from a process, relational and complexity-informed perspective, mobilizing contributions from Psychology. I discuss Psychology’s modes of engagement with Interdisciplinarity and Transdisciplinarity in addressing complex challenges. In this context, I introduce the notion of “dissolution” as an Interdisciplinary and Transdisciplinary relational process supporting the theoretical, methodological and pragmatic enrichment or transformation and increased complexity of different disciplines, bodies of knowledge or modes of knowing. Finally, I propose a new domain for research and practice: a (“Dissolved”) Psychology of Interdisciplinary and Transdisciplinary Relations.