The After Action Review (AAR) is widely acknowledged as a key component of military collective training, which can have a fundamental impact on the quality of training output, which in turn should be reflected in increased performance in operations. The British Army Land Warfare Centre sought to ensure that AARs were being conducted in accordance with accepted best practice, to identify ways of improving the effectiveness of the AAR practice and to inform the process of formalising Observer/Controller training. This paper presents the results of an international review of AAR practice conducted for these purposes. In order to identify areas where improvements could be made, it was necessary to determine what was considered to be "best practice" and how that related to current practice and the AAR experience for those involved in the process. This involved a review of British Army practice and a comparison with the approaches taken by the US Army and the Canadian Army. The study was conducted in two phases. During the first phase, a detailed set of interviews were conducted with British Army ARR participants, including both staff involved in AAR delivery and AAR recipients, during collective training exercises being conducted at a cross section of British Army Collective Training Establishments in the UK and at the British Army Training Unit, Suffield (BATUS) in Canada. During the second phase a similar set of interviews were conducted with AAR participants from the US Army and Canadian Army during collective training exercises being conducted at the National Training Centre, Fort Irwin. The interview results were compared with the findings of a literature review and an evaluation of established doctrine. The paper details the findings of each phase of the study and the final recommendations that were made.