One-size-fits-all taxation fails to accommodate diverse taxpayer circumstances. This Article proposes allowing taxpayers to contract into alternative tax regimes administered by private intermediaries. Participating taxpayers would make payments to the intermediaries pursuant to contract, and the intermediaries would be required to pay to the government at least as much as these taxpayers would have paid the government otherwise. That amount is determined based on the actual tax receipts of a control group, taxpayers who wish to contract with an intermediary but instead are chosen at random to continue under the status quo. These alternative tax regimes might better accommodate taxpayers’ preferences, leaving the taxpayers with greater utility without reducing government revenue. An intermediary could offer different substantive law, different procedural rules, or both. Taxpayers, for example, might receive lower tax rates in exchange for forgoing deductions that cause the taxpayer to engage in socially wasteful behavior. Advances in artificial intelligence make contractual tax reform feasible.