The earliest recorded laws of rugby, written by Rugby School pupils in 1845, are similar to today's rules. The notion of offside, the banning of forward passes and the idea of running a ball out of "touch" all are featured in the early codes. Paintings of early rugby games show dozens of players, instead of the 15 per team today. The rules also controversially promoted "hacking" -- the kicking and tripping of an opponent's legs. This was soon banned and replaced with the shoulder tackles seen in the modern game. Rugby in the 1800s also was far more focused on kicking, rather than the modern aim of try scoring.

The first rugby laws were standardised in 1870 and the International Rugby Football Board (later named the IRB) was formed in 1886. In 1930 the IRFB was made responsible for developing any new laws. These laws have changed over time. The point value for scoring tries has increased from zero to five, penalties were initially worth just two points and drop goals four. The ball has changed too, going from a pig's bladder to a rubber bladder in first a leather case and nowadays, a plastic case, and becoming more oval in shape. Player numbers were initially 20 on each side, but reduced to 15 in 1877.

The laws were still being tweaked in the early twenty-first century, with some of the biggest changes being introduced in 2009.

The experimental law variations (ELVs) were a proposed set of amendments to the laws of rugby union. They were proposed by the sport's governing body, the International Rugby Board (IRB), and trialled games at Stellenbosch University in 2006. In 2008 thirteen of the 23 variations trialled were played globally including; greater responsibility for assistant referees, corner posts no longer considered to touch in-goal, no gain in ground if the ball is moved into the 22-metre line by a player from the same team as the kicker, quick throw-ins can travel backwards, no restrictions to players in the lineout, restrictions on where receivers and opposition hookers can stand in a lineout, pregripping and lifting allowed, mauls can be pulled down and players can enter with their head and shoulders lower than their hips, offside line is five metres away from the scrum for the backs and scrum half must be positioned close to the scrum, all offences apart from foul play and offsides are a free kick, and unplayable rucks and mauls are restarted with a free kick.

In 2009 the IRB approved ten of the laws, rejecting the laws relating to mauls, numbers in a lineout and the increase in sanctions punishable by free kicks.