A clear-eyed study that reveals how politics shapes and often distorts important federal programs, driving inequalities across states. From Medicaid to Section 8 Housing Choice Vouchers, a large percentage of the annual US federal budget (approximately $1 trillion) is distributed through grants-in-aid, a policy tool that allocates aid to state and local governments rather than to individual Americans. When members of Congress use grants-in-aid to fund healthcare, housing, and other forms of support, they are not solely determining how much assistance one person receives. Instead, they can allot certain localities larger grants, which carry big implications for the quality of public services available to citizens living in different states. Many reasonably assume that these assistance programs distribute funding to states impartially because they use statistical formulas based on population levels, poverty, and other characteristics that, ostensibly, measure need. However, in Politics by Formula, Leah Rosenstiel shows how this seemingly technocratic aspect of federal policymaking is deeply affected by both the structure of political institutions and the motivations of elected officials. Key congressional committees—and especially their leaders—design formulas to benefit their constituencies. Superficially neutral formulas can shield these political decisions from scrutiny, but formulas also constrain congressmembers. Drawing on formal modeling and quantitative and qualitative evidence, Rosenstiel elucidates how these dynamics shape whose and what needs are met and where.