During the first months of the American Civil War, an important political debate played out in the U.S. Congress over how to restructure the nation’s system of public finance and taxation. The fiscal crisis occasioned by the military conflict forced Republican leaders (who dominated our national political institutions) to adopt drastic and controversial measures including the expansion of public borrowing, the issuance of a national paper currency (so-called Greenbacks), and the adoption of a national income tax. To be sure, there was widespread resistance within the Republican Party to all of these proposals—most particularly, the income tax. Unsurprisingly, conservative Republicans from the Northeast adamantly opposed the impost. Despite this opposition, a majority of Republicans eventually acquiesced to this “odious” tax based on the need to fund the Union war effort. A number of key Republican leaders in Congress preferred this impost over the alternatives (in particular, a national land tax), casting their arguments in favor of the income tax in terms of “equity,” “justice,” and “fairness.” Based on their support, Congress approved a national income tax, signed into law by President Lincoln on August 5, 1861. While the war effort was largely funded by public borrowing and increases to tariff rates, the income tax made a modest contribution to financing the Northern military campaign and emerged as an important component in the reconstituted wartime fiscal system. Although the impost was allowed to expire soon after the resolution of the military conflict, the Civil War income tax served as the model for the modern income tax enacted by Congress more than 40 years later. Likewise, in the debate over our nation’s first income tax, we hear the first articulations of arguments resurrected during the debate over the income tax of 1913 as well as in contemporary political discourse over federal tax policy.