Mergers and acquisitions (M&A) are often defended as instruments for improving an acquiring company’s operating efficiency through economies of scale, complementary assets, stronger market access, technology transfer, and the redeployment of capital. Yet an increase in size, revenue, or market share does not necessarily demonstrate that the acquisition has made the acquirer more productive. This paper examines the relationship between M&A and the operating efficiency of Indian acquiring companies through doctrinal analysis, a review of empirical literature, and comparative case studies. It considers the statutory process under the Companies Act, 2013, competition review under the Competition Act, 2002, and related securities, tax, and sectoral constraints. The literature on Indian firms is mixed: some studies find improved profitability and cash-flow margins, while others show deterioration in raw post-merger metrics or no significant improvement after adjusting for the performance of comparable firms. The paper analyses Tata Motors’ acquisition of Jaguar Land Rover, Hindalco’s acquisition of Novelis, Sun Pharmaceutical Industries’ acquisition of Ranbaxy, and the merger of HDFC Limited into HDFC Bank. These examples show that operating results depend on the fit between strategic rationale and integration design, financing structure, regulatory compliance, organisational capability, and the time horizon used to assess performance. The paper argues that efficiency must be treated as a testable post-closing outcome rather than a presumption arising from deal completion. It recommends measurable synergy baselines, independent monitoring, transparent disclosure, competition-sensitive planning, and multi-year evaluation against industry and control-firm benchmarks.