MERGERS AND acquisition (‘M&A’) transactions, widely discussed in the media, have expanded tremendously over the years, both in the number of deals and in financial volume, becoming an important aspect of national and international economic transactions. Many have raised competition law issues and caused political controversy. Furthermore, these transactions have frequently triggered disagreements between the parties involved, a fair number ending up in arbitration, with considerable amounts in dispute. This article will focus on the issue of purchase price adjustment, discussing some of the typical features of these disputes, including aspects such as contract drafting, recourse to experts on accounting issues, and the role of arbitration tribunals. Very schematically, M&A transactions can be described as processes that, frequently after a bidding involving interested buyers, start with a negotiated letter of intent, in which the parties express their interest and usually their commitment to a deal and set a framework for the transaction. Subsequently, detailed and often complex negotiations take place between the parties, accompanied by due diligence, leading up to the execution of a purchase agreement that will state a provisional price as well as adjustment mechanisms and procedures. Generally, and ideally, full due diligence is performed before contract signing in order to assess all relevant economic and financial aspects of the target company and to draft the appropriate representation and warranty provisions. Finally, ‘closing’ of the transaction takes place. This is the moment when the shares or title documents are delivered against the payment. Thereafter, a ‘closing balance sheet’ or other reference factors, such as the target company's earnings, will be established and serve as the basis for price adjustment.