Since they were folk games, the early games had no 'official' rules, and they tended to change over time. To the extent that there were rules, they were generally simple and were not written down. There were many local variations, and varied names.

Many of the early games were not well documented, first, because they were generally peasant games (and perhaps children's games, as well); and second, because they were often discouraged, and sometimes even prohibited, either by the church or by the state, or both.

Aside from obvious differences in terminology, the games differed in the equipment used (ball, bat, club, target, etc., which were usually just whatever was available), the way in which the ball is thrown, the method of scoring, the method of making outs, the layout of the field and the number of players involved.

An old English game called "base," described by George Ewing at Valley Forge, was apparently not much like baseball. There was no bat and no ball involved! The game was more like a fancy game of "tag", although it did share the concept of places of safety (ie, bases) with modern baseball.

In an 1801 book entitled The Sports and Pastimes of the People of England, Joseph Strutt claimed to have shown that baseball-like games can be traced back to the 14th century, and that baseball is a descendant of a British game called stoolball. The earliest known reference to stoolball is in a 1330 poem by William Pagula, who recommended to priests that the game be forbidden within churchyards.

In stoolball, a batter stood before a target, perhaps an upturned stool, while another player pitched a ball to the batter. If the batter hit the ball (with a bat or his/her hand) and it was caught by a fielder, the batter was out. If the pitched ball hit a stool leg, the batter was out. It was more often played by young men and women as a sort of spin the bottle.

According to many sources, in 1700, a Puritan leader of southern England, Thomas Wilson, expressed his disapproval of "Morris-dancing, cudgel-playing, baseball and cricket" occurring on Sundays. However, David Block, in Baseball Before We Knew It, reports that the original source has "stoolball" for "baseball". Block also reports that the reference appears to date to 1672, rather than 1700.

A 1744 publication in England by John Newbery called A Little Pretty Pocket-Book includes a woodcut of stoolball and a rhyme entitled "Base-ball." The book was later published in Colonial America in 1762. In 1748, the family of Frederick, Prince of Wales partook in the playing of a baseball-like game.

A 1791 bylaw in Pittsfield, Massachusetts bans the playing of baseball within 80 yards of the town meeting house.

Les Jeux des Jeunes Garçons is the first known book to contain printed rules of a bat/base/running game. It was printed in Paris, France in 1810 and lays out the rules for "poison ball," in which there were two teams of eight to ten players, four bases (one called home), a pitcher, a batter, and flyball outs.

Another early print reference is Jane Austen's posthumous 1818 novel Northanger Abbey.

In 1829, William Clarke in London, published The Boy’s Own Book which included rules of rounders. Similar rules were published in Boston, Massachusetts in 1834, except the Boston version called the game "Base" or "Goal ball." The rules were identical to those of poison ball, but also added fair and foul balls and strike outs.

The account by Fred Lillywhite (1829-66) of the first English cricket tour to Canada and the United States in 1859 refers to the "base-ball game [being] somewhat similar to the English game of "rounders"". A day's play was lost during a cricket match in New York due to snow, but a game of baseball was arranged about a mile away between "the players of that game and a portion of the English party" (The English Cricketers' Trip to Canada and the United States, 1860).

The legend of Doubleday’s invention of baseball was itself baseball's invention, in a sense that of Al Spalding, a former star pitcher, then club executive, who had become the leading American sporting goods entrepreneur and sports publisher. Debate on baseball origins had raged for decades, heating up in the first years of the 20th century. To end argument, speculation and innuendo, Spalding organized a panel in 1905. The panelists were his friend Abraham G. Mills, a former National League president; two United States Senators, ex-NL president Morgan Bulkeley and ex-Washington club president Arthur Gorman; ex-NL president and lifelong secretary-treasurer Nick Young; two other star players turned sporting goods entrepreneurs (George Wright and Alfred Reach); and AAU president James E. Sullivan.

The final report published in 1908 included three sections: a summary of the panel’s findings written by Mills, a letter by John M. Ward supporting the panel, and a dissenting opinion by Henry Chadwick. The research methods were, at best, dubious. The Mills Commission probably looked for and found the perfect story: baseball was invented in a quaint rural town without foreigners or industry, by a young man who later graduated from West Point and served heroically in the Mexican-American War, Civil War, and U.S. wars against Indians.

The Mills Commission concluded that baseball had been invented by Doubleday in Cooperstown, New York in 1839; that Doubleday had invented the word baseball(?), designed the diamond, indicated fielder positions, written down the rules and the field regulations. However, no written records from 1839 or the 1840s have ever been found to corroborate these claims; nor could Doubleday be interviewed for he died in 1893. The principal source for the story was a letter from elderly Abner Graves, a five-year-old resident of Cooperstown in 1839. But Graves never mentioned a diamond, positions or the writing of rules. Graves' reliability as a witness has also been questioned because he was later convicted of murdering his wife and spent his final days in an asylum for the criminally insane. Further, Doubleday was not in Cooperstown in 1839. He was enrolled in West Point and there is no record of any leave time. Mills, a lifelong friend of Doubleday, had never heard him mention inventing baseball.

As noted previously, versions of baseball rules have since been found in publications that significantly predate the alleged invention in 1839.

Jeff Idelson of the Baseball Hall of Fame in Cooperstown, New York has stated, "Baseball wasn't really born anywhere," meaning that the evolution of the game was long and continuous and has no clear, identifiable single origin.

The role of Cartwright himself is disputed; his authorship is sometimes called a significant exaggeration, a modern attempt to identify a single "inventor" of the game, thereby akin to the Doubleday myth. He was at least secretary for a group effort. One point undisputed by historians is the direct evolution from amateur urban clubs of the 1840s and 1850s, not the pastures of the small Cooperstowns of America, to the modern professional major leagues that began in the 1870s.

Before 1845
Evolution of the game that became modern baseball is unknown before 1845. The Knickerbocker Rules describe a game that they had been playing for some time. But how long is uncertain and so is how that game had developed.

There were once two camps. One, mostly English, asserted that baseball evolved from a game of English origin (probably rounders); the other, almost entirely American, said that baseball was an American invention (perhaps derived from the game of one ol' cat). Apparently they saw their positions as mutually exclusive. Some of their points seem more national loyalty than evidence: Americans tended to reject any suggestion that baseball evolved from an English game, while some English observers concluded that baseball was little more than their rounders without the round.

Cricket and Rounders
That baseball is based on English and Gaelic games such as cat, cricket, and rounders is difficult to dispute. On the other hand, baseball has many elements that are uniquely American.

Certainly baseball is related to cricket and rounders, but exactly how, or how closely, has not been established. Modern cricket is much older than modern baseball.

People have been playing games with balls or bats or bases for millennia, probably, and playing games with two of those elements for centuries before the Knickerbockers, certainly. Games played with bat-and-ball together may all be distant cousins; the same goes for base-and-ball games. Bat, base, and ball games for two teams that alternate in and out, such as baseball, cricket, and rounders, are likely to be close cousins. They all involve throwing a ball to a batsman who attempts to "bat" it away and run safely to a base, while the opponent tries to put the batter-runner out when liable ("liable to be put out" is the baseball term for unsafe).

After 1845
In 1857, sixteen clubs from modern New York City sent delegates to a convention that standardized the rules, essentially by agreeing to revise the Knickerbocker rules. In 1858, twenty-five including one from New Jersey founded a going concern but the National Association of Base Ball Players is conventionally dated from 1857. It governed through 1870 but it scheduled and sanctioned no games.

By 1862 some NABBP member clubs offered games to the general public in enclosed ballparks with admission fees.

During and after the American Civil War, the movements of soldiers and exchanges of prisoners helped spread the game. As of the December 1865 meeting, the year the war ended, there were isolated Association members in Fort Leavenworth (Kansas), St. Louis, Louisville, and Chattanooga, Tennessee, along with about 90 members north and east of Washington.

In 1869 the first openly professional baseball team formed. Earlier players were nominally amateurs. The Cincinnati Red Stockings recruited nationally and effectively, toured nationally, and no one beat them until June 1870.

Already in the 19th century, the "old game" was invoked for special exhibitions such as reunions and anniversaries — and for making moral points. Today hundreds of clubs in the U.S. play "vintage base ball" according to the 1845, 1858, or later rules (up to about 1887), usually in vintage uniforms. Some of them have supporting casts that recreate period dress and manner, especially those associated with living history museums.