The British military spent 20 years, between 7 October 2001 and 28 August 2021, fighting in Afghanistan. Considering the UK’s achievements against its objectives, defeat seems the most accurate description of the engagement’s outcome. How institutions respond to and learn from failure is a good measure of their effectiveness. In the British military learned over the course of the Afghanistan campaign many valuable and hard-won lessons. Such lessons have significant relevance to wider defence issues and should be studied specifically as they relate to British strategy and the tactical execution of military operations. There have also been lessons that still need to be learned. many rich and important lessons can be derived from a careful study of British operations in Afghanistan. Whether these and other lessons can be learned will be critical in determining the success or failure of campaigns well into the future.