This chapter explores the enduring legacy of the Iraq War for the US and UK, exploring the themes that have endured in the twenty years since the invasion. This chapter outlines what impact the Iraq War has on contemporary politics and policymaking in Washington and London, before examining how policymakers have sought to learn the lessons from the decision to invade Iraq. This section argues that whilst significant resources and time have been devoted to highlighting these lessons, very few have been implemented and actually “learned”. I start the chapter by asking, how the Iraq War is understood in the US and the UK? To answer this, I explore the many investigations into the decision processes in Washington and London, such as the Kerr Report, the Butler Inquiry, and the Chilcot Inquiry. In doing so, I demonstrate the similarities and differences between these understandings of the legacy. Following this, I ask, how has this understanding manifested in foreign policymaking? I explore how the legacy affected relations with allies and enemies, how this affected subsequent military interventions in public and policy discourse. I follow this with an exploration of the lessons that have been drawn from the experiences of deciding to invade Iraq. I highlight how these lessons have been drawn from the experience, and why many have not been “learned” or implemented. This chapter concludes with a discussion of why these lessons have not been learned, and what the enduring legacy of the Iraq invasion is in contemporary US and UK foreign policy debates. In doing so, this chapter demonstrates how there has been much more attention on lesson learning in London than in Washington. Yet, despite this greater engagement and expense, neither the UK government nor the US government has learned these lessons from the experience of invading Iraq.