Risk-based rules are the tax system’s primary response to aggressive tax planning. They usually grant benefits only to those taxpayers who accept risk of changes in market prices (market risk) or business opportunities (business risk). Attempts to circumvent these rules by hedging, contractual safeguards, and diversification are well understood. The same cannot be said about a very different type of tax planning. Instead of reducing risk directly, some taxpayers change the nature of risk. They enter into informal, legally unenforceable agreements with contractual counterparties that are designed to eliminate market or business risk entirely. The new uncertainty these tax planners inevitably accept, however, is the risk that the counterparties will violate the implicit agreements and betray taxpayers’ trust (counterparty risk). A deliberate substitution of counterparty risk for market or business risk is what this Article calls relational tax planning. The Article offers an economic analysis of different risks and considers two responses to the relational tax planning problem. The analysis suggests that from a welfarist perspective, business risk is a superior deterrent compared to both market and counterparty risks. Counterparty risk is the most complex of the three. In addition to producing risk-bearing losses like all other risks, it leads to reduced transaction costs in future exchanges between relational tax planners, but only if they manage to overcome bargaining obstacles caused by opportunism and asymmetric information. These insights suggest two very different responses. A sweeping reform will allow—and even encourage—taxpayers to engage in relational tax planning, but it will also ensure that counterparty risk they incur is sufficiently high. If only incremental improvements are pursued, courts should increase their scrutiny of relational tax planning involving extensive dyadic business relationships and interactions based on social norms.