On 23 February 2012, ESMA published a discussion paper on key concepts of the Alternative Investment Fund Managers Directive and types of AIFM, which was followed on 19 December 2012 by the publication of a consultation paper on guidelines on key concepts of the AIFMD. The consultation set out formal proposals for guidelines ensuring common, uniform and consistent application of the concepts in the definition of ‘AIF’ in Article 4(1)(a) of the AIFMD by providing clarification on each of these concepts. This final report contains an explanation of the concepts used in the definition of an AIF, including the meaning of collective investment undertaking, raising capital, and the number of necessary investors.