munications "firms to share the source of their advantage is in some tension with the underlying purpose of antitrust law, since it may lessen the incentive for the monopolist, the rival, or both to invest in those economically beneficial facilities" (540 U.S. 398, 407-08 (2004)). Policymakers were able to ignore the impact on investment in new networks when entry by new networks was infeasible. That is no longer the case today, now that digitization has broken down the barriers between communications technologies, new media (such as wireless) have emerged as important modes of transmission, and upgrading network technology has become an important way in which firms compete. Indeed, industry analysis must take into account the increasing complexity of communications technology. Our analysis has largely been in the context of what are frequently called "managed networks," in which a handful of large actors make decisions about network boundaries and interconnections. The Internet operates on distinctly different principles. Because it is composed of a large number of autonomous systems, decisions about network configuration will be made in a more decentralized and uncoordinated manner. The shift to this more diffuse mode of governance will bring communications networks within the domain of what are often called "spontaneous networks," in which each node has the potential to act independently. Understanding market outcomes when there are spontaneous networks requires an analysis of the incentives confronting each individual node. This transformation will make analytical frameworks that capture the interaction among different network elements all the more essential to understanding network behavior and the impact of mandating access in the years to come. Recognizing the complexity of networks strongly suggests the need for regula- tory forbearance. The complexity of networks implies that policymakers cannot be Networks in Telecommunications expected to design ideal network configurations. The effects of public polic