Softball is a variation of baseball, the difference being that it is played with a larger ball, on a smaller field, and with only underhand pitches permitted; where the ball is released while the hand is primarily below the ball. Softball is played competitively at club levels, the college level, Olympic level and the professional level. The game was created in 1887 in Chicago by George Hancock.

There are two rule sets for softball generally: slow-pitch softball and fastpitch. Slow-pitch softball is commonly played recreationally, while women's fastpitch softball was a Summer Olympic sport and can be played professionally. Softball was not included in the 2024 Summer Olympics but will return for the 2028 Summer Olympics.

Depending on the variety being played and the age and gender of the players, the particulars of the field and equipment will also vary. While distances between bases of 60 feet (18 m) are standard across varieties, the pitcher's plate ranges from 35 to 43 feet (10.7 to 13.1 m) away from home plate, and the home run fence can be 220 to 300 feet (67 to 91 m) away from home plate. The ball itself is typically 11 or 12 inches (28 or 30 centimetres) in circumference, though this also depends on specifics of the competition. Softball rules vary in certain aspects from those of baseball. The game moves at a faster pace than traditional baseball due to the field being smaller and the bases and the fielders being closer to home plate. Softball is pitched underhand from flat ground, whereas baseball is pitched overhand from a raised pitcher's mound.

The earliest known softball game was played in Chicago, Illinois, on Thanksgiving Day, 1887. It took place at the Farragut Boat Club at a gathering to hear the outcome of the Yale University and Harvard University football game. When the score was announced and bets were settled, a Yale alumnus threw a boxing glove at a Harvard supporter. The Harvard fan grabbed a stick and swung at the rolled-up glove. George Hancock, a reporter there, called out "Play ball!" and the game began, with the boxing glove tightened into a ball, a broom handle serving as a bat. This first contest ended with a score of 41–40. The ball, being soft, was fielded barehanded.

Hancock is credited as the game's inventor for his development of a 17-inch ball and an undersized bat in the next week. The Farragut Club soon set rules for the game, which spread quickly to outsiders. Envisioned as a way for baseball players to maintain their skills during the winter, the sport was called "Indoor Baseball". Under the name of "Indoor-Outdoor," the game moved outside in the next year, and the first rules were published in 1889.

In 1895, Lewis Rober Sr. of Minneapolis organized outdoor games as exercise for firefighters; this game was originally known as kitten ball. Rober's version of the game used a ball 12 inches (30 cm) in circumference, rather than the 16-inch (41 cm) ball used by the Farragut club, and eventually the Minneapolis ball prevailed, although the dimensions of the Minneapolis diamond were passed over in favor of the dimensions of the Chicago one. Rober may not have been familiar with the Farragut Club rules. Fire Station No. 19 in Minneapolis, Rober's post from 1896 to 1906, was listed on the National Register of Historic Places in part for its association with the sport's development. The first softball league outside the United States was organized in Toronto, Ontario, in 1897.

The name "softball" dates back to 1926. The name was coined by Walter Hakanson of the YMCA at a meeting of the National Recreation Congress. (In addition to "indoor baseball", "kitten ball", and "diamond ball", names for the game included "mush ball", and "pumpkin ball".) The name softball had spread across the United States by 1930. By the 1930s, similar sports with different rules and names were being played all over the United States and Canada. A tournament held in 1933 at the Chicago World's Fair spurred interest in the game. By 1936, the Joint Rules Committee on Softball had standardized the rules and naming throughout the United States. In this decade, American women transitioned from playing feminized versions of baseball to mainly playing softball.

Sixteen-inch softball, also sometimes referred to as "mush ball" or "super-slow pitch" and is a direct descendant of Hancock's original game. Defensive players are not allowed to wear fielding gloves. Sixteen-inch softball is played extensively in Chicago, where devotees such as newspaper columnist Mike Royko consider it the "real" game, and New Orleans. In New Orleans, sixteen-inch softball is called "Cabbage Ball" or "batter ball" and is a popular team sport in area elementary and high schools.