As markets change due to new technologies, shifts in consumer preferences or other conditions, the legal and policy framework need to adjust, too. The dilemma legislators and policy makers face when such changes take place is whether and how to intervene in such market situations and if they intervene, what respective roles regulation and competition law should play.

There is a renewed interest in discussing and even reconceptualizing this relationship in light of current challenges such as the financial crisis, climate and health crisis, digitalization and rising corporate and political power. This chapter analyses how market power is controlled at the intersection between competition law and regulation in EU competition law and in US antitrust law. It traces back how this complex interplay has evolved in these two jurisdictions as well as look forward how this interface is changing in current law and policy making processes.