This Article surveys the history of the U.S. income tax system from 1913 to the present, examining changes in the structure of the graduated rates system over the past 100 years, using inflation-adjusted dollars. By connecting these changes to key events in the history of the United States, the Article contextualizes modifications Congress has made to the income tax over time as well as the current debate surrounding several proposals for reform. First, the Article demonstrates that the rate structure has become more flat (with lower rates and fewer brackets than in the past), compressed (with less graduation, steeper jumps between brackets, and less penetration of the rate schedule into the income strata), and complex (with the proliferation of tax expenditures) over time. Second, the Article reveals that the structures that would result from two of the tax reform proposals being discussed in the popular media resemble historical rates and brackets. Because these proposals for tax reform have analogs in earlier versions of the income tax, the Article argues that analysis of economic data from prior periods may help inform tax policy and identifies an agenda for future research.