The Indiana pi bill was bill #246 of the 1897 sitting of the Indiana General Assembly, one of the most notorious attempts to establish mathematical truth by legislative fiat. Despite its name, the main result claimed by the bill is a method to square the circle, although it does imply various incorrect values of the mathematical constant π, the ratio of the circumference of a circle to its diameter. The bill, written by a physician who was an amateur mathematician, never became law due to the intervention of C. A. Waldo, a professor at Purdue University, who happened to be present in the legislature on the day it went up for a vote.

Squaring the circle is a problem in geometry first proposed in Greek mathematics. It is the challenge of constructing a square with the area of a given circle by using only a finite number of steps with a compass and straightedge. The difficulty of the problem raised the question of whether specified axioms of Euclidean geometry concerning the existence of lines and circles implied the existence of such a square.