This thesis examines how Big Tech firms consolidate market power in digital markets through killer acquisitions and strategic partnerships, and how these strategies challenge the effectiveness of the European Union (EU) merger control regime. Although differing in legal form, both exploit similar weaknesses of the EU Merger Regulation (EUMR). The thesis argues that EU merger control is poorly adapted to digital markets. Turnover-based jurisdictional thresholds fail to capture killer acquisitions involving low-revenue but strategically important firms, while the Significant Impediment to Effective Competition (SIEC) test is ill-suited to low-probability but high-impact harm. In response, the thesis advocates reform in the form of a strengthened use of Article 22 referrals and a recalibration of the substantive assessment through a balance of harms approach. It further shows that strategic partnerships frequently escape merger control because they do not qualify as concentrations under the EUMR, despite being functionally equivalent to them. The thesis assesses the Digital Markets Act (DMA) as a tool complementing merger control but finds that it primarily enhances transparency and does not close these gaps. Overall, the thesis concludes that the existing EU merger control regime remains limited in addressing competitive risks arising in digital markets.