Consideration of the relationship between trauma and homelessness has traditionally been a marginal area of concern in Australian research and policy, and an informal, if nonetheless daily, concern in face-to-face work with those living homeless. Currently, however, trauma is being positioned nationally and internationally as a critical lens to use in homelessness research, policy and service revitalisation. To understand these emerging trajectories of trauma-informed concern ·at research, policy and practice levels, it is important to engage with the existing base of interdisciplinary knowledge, which examines the relationship between experiences of trauma and experiences of homelessness. This chapter provides an introductory overview of what trauma is and why trauma can usefully be considered an important cause and consequence of homelessness. Its aim is to explore how trauma is implicated in both triggering specific episodes of homelessness and structuring long-term vulnerability to homelessness. Further, both being homeless and the higher risk contexts of homelessness are explored as primary sources of trauma and re-traumatisation. In exploring the argument that trauma and homelessness are closely intertwined, it is important to consider how researchers define the core concepts they work with and to appreciate the contested nature of these. Thus, before tracing arguments about the ways in which homelessness trauma may intersect to deepen vulnerability, some of the ways which 'trauma' and 'homelessness' have been generated as broad organising categories for diverse experiences will be explored. The chapter concludes with a brief consideration of the value of trauma-informed care provision in homelessness services.