This master thesis deals with the accounting of mergers and acquisitions (M&As) as well as with the post-implementation review (PIR) of IFRS 3 business combinations by the IASB. Therefore, the purposes are to identify the main implementation challenges or unexpected costs and identify possible measures of the current standard. In the first part, a general introduction to M&As is given, focusing on different forms of M&As and the development, relevance and subprocesses of M&As-deals. In order to obtain information about current problems of IFRS 3, comment letters of different organisations and institutions, reports and discussions of different IASB-meetings, findings and an academic literature review were used. In the final part, the results of the empirical research are presented and discussed. The most significant areas of IFRS 3-challenges are the following: the complexity of testing goodwill for impairment, challenges in applying the definition of a business, the identification and fair value measurement of intangible assets such as customer relationships and brand names. For these challenges, the IASB has to intensify the work with the FASB and consider improvements to the problems.