Can a multilateral negotiating process—that is, cooperation between many states in a single forum—successfully reform the network of bilateral tax treaties that currently makes up the bulk of international tax law? The BEPS Project aims to be the first major push for a multilateral tax process since the creation of the OECD’s Model Tax Convention in the 1960s. Through BEPS, the OECD and 130-plus countries are in final negotiations to implement Pillar One and Two, which will: (1) create a new taxing right for “market jurisdiction” countries on the profit of international companies that do business there without a physical presence; and (2) implement a top-up tax levied against companies that offshore profits from intangible assets in low-tax jurisdictions. To predict whether the multilateral reform effort will be successful, it is important to examine the nature of the multilateral negotiating process itself, because every negotiation is shaped by its context.  But this context is not static—rather, the nature of tax multilateralism varies depending on certain global conditions. Sometimes, it is a hierarchical process, dominated by powerful countries operating in a closed-club of developed states spearheading the effort, while weaker countries must tag along and accept the eventual outcome. Alternatively, multilateralism may be egalitarian and inclusive, with many countries—strong and weak alike—contributing to the debate, accepting tradeoffs, and endorsing the outcome. In this thesis, I demonstrate that the nature of tax multilateralism has changed from the former model to the latter by comparing the negotiation of the OECD Model Tax Conventions with the Pillars Negotiation. I begin by identifying several factors that influence the nature of tax multilateralism: first, the distribution of global power among states; and second, the level of integration of the global economy. In an international system where power is concentrated in a few states, and the international economy is fragmented (i.e., the conditions of the 20th Century), multilateralism tends to be hierarchical and exclusive. However, when power is diffused and the global economy is integrated, (the conditions of the 21st Century), then multilateralism is egalitarian and inclusive. In such a context, international tax issues—like base erosion and profit-shifting—are so vast and complex that no state, acting alone or in a small group, could deal with them. The thesis thus concludes that the nature of tax multilateralism has changed, because in modern negotiations, powerful states are both less capable of dominating other states in the negotiating process and are highly dependent on a successful outcome that creates global consensus.