Academic studies of sustainable fashion, and the discourses of actors in business and policy, under-define fashion as a system by treating the social and ecological aspects of fashion separately. This reduces the potential for academic findings to provide knowledge useful for transformation of the fashion system and obstructs desired outcomes from policy and business responses to fashion’s negative social and environmental impacts. Understanding how fashion works as a system presents a challenge to transdisciplinary efforts for transformation towards sustainability. In this Licentiate, I explore ways to look at fashion using a feminist critical realist social-ecological system approach. I develop a theoretical framework to understand the fashion system, and particularly to understand what is keeping it unsustainable. I view fashion as a ‘nested’ social-ecological system with inseparable social and biophysical parts.  I use a feminist lens characterized by diversity; this draws attention to gaps, what is known, missing and absent. To show that social aspects and material aspects are intertwined and cannot be studied independently of each other, I use critical realism as a metatheory. I bring its idea of a stratified reality and the model of the four-planar social being to the social-ecological system approach that forms the core of my work. I combine Ostrom’s frequently used general framework for analysing social-ecological systems with a policy-oriented framework for sustainable development. Drawing from these two frameworks I develop a five principles for a strategy framework for sustainable fashion. In summary, applying the strategy framework within the theoretical framework enables thinking more deeply about the structure and implications of knowledge contributions when taking a social-ecological perspective on actions for sustainability.  The two papers in this licentiate thesis examine the effects of ontological standpoints that allow environmental impacts of textile fibres to be analysed in isolation from the cultural and social aspects of fashion.    Paper 1, ‘Making Resilient Decisions for Sustainable Circularity of Fashion’, is recently published in the journal Circular Economy and Sustainability (Palm et al. 2021). It aimed to show how current circularity responses to global sustainability challenges have so far fallen short. The current path of the expanding fashion industry is fraught with accelerated material throughputs and increased disposal and waste, contributing to human-driven environmental changes at planetary scale. In addition the fashion industry has issues of poor working conditions, modern-day slavery, and justice. By representing a Driver – State – Response framework as an adaptive cycle of a social-ecological system, it makes it clear that reducing planetary pressure from the global fashion and textiles industry requires greater recognition of the system’s social drivers. This paper was a step towards the iterative development of my sustainable fashion framework.   Paper 2, ‘Reviewing and defining the concept of Sustainable Fashion: a critical social-ecological approach’, is included as an early-stage draft manuscript. It aims to provide a starting point for discussions towards a coherent science-business-policy definition of the concept of sustainable fashion itself. Using the five theoretically grounded principles of my strategy framework, I examine the manifold definitions related to sustainable fashion such as eco fashion, green fashion, ethical fashion, slow fashion, organic fashion and cradle-to-cradle-fashion. Critical realism’s idea of absence structures this paper.  This thesis contributes to knowledge of what a nested inseparable social-ecological system fashion is, enriching ontological descriptions for resilience research more generally.  Also, it provides concrete guidance for transdisciplinary efforts with business and policy working to decrease fashion’s negative impacts on humans and the planet, by showing that fruitful responses pay attention to social activities beyond the industry value chain, not just material flows within. Finally,  I hope my research serves as a contribution to propaedeutics of the field of sustainable fashion, i.e. giving an introductory understanding of the reality and the possibilities of fashion for people and planet. / <p>The work presented here was part of a consortium research project between Stockholm Resilience Centre and the Ellen MacArthur Foundation, initiated and funded by H&amp;M Group, the Swedish public limited company. Celinda Palm, Sarah Cornell and Tiina Häyhä’s employment was part-funded through this project.</p>