Baseball around the world is played under three major rules codes, which differ only slightly. The North American professional leagues and many amateur leagues use the Official Baseball Rules, which are published to the public by The Sporting News; U.S. collegiate and college-age play is often covered by the baseball rulebook of the NCAA; and U.S. high school and high school-age baseball is governed by the NFHS rules. IBAF international teams, most leagues outside North America, and youth baseball organizations such as Little League, PONY League, and Cal Ripken League all play under slightly modified versions of the Official Baseball Rules.
Unlike many other sports, the Official Baseball Rules have remained largely static during the modernization of the game. This is evidenced in much esoteric or awkward language in the rulebook; also, rules experts such as Chris Jaksa and Rick Roder have identified over 50 outright errors in the book, mostly concerning rare or subtle differences. Many baseball players, fans, and administrators view the rules and traditions of professional baseball as time-tested and nearly sacrosanct. The designated hitter rule, first introduced to play over 30 years ago in 1973, is still subject to lively debate and has been adopted by only one of the two American major leagues and one of the two Japanese major leagues — though almost all other leagues around the world have adopted it. In fact, NFHS rules allow the designated hitter to bat for any position. In contrast to the Official Baseball Rules, the NFHS is continually refining and updating its rule book to meet the needs of the United States high school game. The NCAA updates its rulebook less often the NFHS, but still more current.
However, the static nature of the rules has also been a source of the sport's appeal to many fans, as it allows reasonable comparisons to be drawn between players and teams of different eras. Such comparisons are not possible in sports in which the rules have changed significantly over the years. The static nature of the rules also allows a modern fan to easily follow an account of a game played long ago. As a result, baseball has more of a "history" than most other sports. As an illustration of this, many newspaper sports sections publish a small This Day in Baseball History feature with highlights of games played as far back as 100 years or more.
In Japan, if a regular-season game is tied after nine innings, only three extra innings may be played. The accepted codes of etiquette also differ in Japanese baseball, though these are not written in official rules.
Other major differences often center around additional safety rules. Most amateur leagues prohibit malicious contact by runners, are stricter on interference calls, and require double-earflap helmets.
For an overview of the rules themselves, see Main article: baseball, the baseball rules category below, or each individual rule book.