Based on extensive firm-level data, the present thesis investigates certain aspects of trade and antitrust regimes, as well as their interplay in the shaping of competitive markets. The first chapter provides evidence on the impact of trade and competition policy reforms in the emergence of competitive pressure across seven transition economies. Chapter 2 tests the conventional wisdom that merger-driven market concentration has a negative impact on competitors' incentives to pursue productive efficiency. While we do find some evidence to that effect with proxies for overall industry consolidation, the takeover-related component is found to trigger the opposite, albeit much more modest, response. Chapter 3 explores the heterogeneous firm underpinnings of world trade, questioning the presence of relative productive efficiency thresholds stipulated in recent theoretical frameworks. Although first-order conjectures are largely in line with the data, our findings don't lend support to a threshold-type relationship and suggest scope for theoretical fine-tuning