Since mergers and acquisitions (M&A) are publicly observable and require a significant amount of acquirer resources, they tend to attract the academic community attention. Do M&As allow an efficient resource allocation across the economy? Do we observe a net wealth creation or is it a mere transfer from one agent to another? The current literature reveals a widespread consensus about the positive impact of the M&As on the shareholder value, at least from the view point of the target firms. But when we broaden the analysis including other stakeholders, the results are more mixed. Evidence on the impact on labor depends on the regulatory framework. If we study the impact on consumers, results are either neutral or positive. Last, M&As seem to foster more focused innovation.