The EU Merger Regulation (EUMR) provides the European Commission with exclusive jurisdiction to assess mergers, acquisitions and full-function joint ventures with an EU dimension on the basis of turnover-based thresholds. The EUMR also contains corrective mechanisms allowing the Commission, under certain circumstances, to review smaller transactions. Until recently, these corrective measures have not been frequently applied but the picture is changing. The Commission believes that market developments (particularly in digital and pharma markets) are resulting in more acquisitions of companies that play or may play a significant competitive role in the EU despite generating little or no turnover. Similar considerations may apply to companies with valuable assets, intellectual property rights, data or infrastructure. This article analyses the development in the Commission’s guidance instruments which look to give merging parties a sense of the circumstances in which smaller deals may be referred by Member States to the Commission for EUMR assessment (mindful though that these developments may yet be checked by the EU's highest court). Legislation has also been evolving at the Member State level (e.g., recently in Ireland) to allow national competition authorities to review sub-threshold deals. This article also provides a comparison of the EU system with certain other non-EU ‘callin’ systems and which reflects that merging parties have an increasingly complex merger control picture to navigate in 2024 and beyond before they can safely implement deals (such as in digital and pharma deals).