Barry Rhodes author of 999 Questions On The Rules of Golf tells us how the Royal & Ancient in St. Andrews became responsible for administering the Rules of Golf.
He explains how in the eighteenth and nineteenth centuries there were many different rules, as each Club developed had their own versions. This obviously led to difficulties and in 1897, by common agreement of the existing clubs, most of who were in Britain, the Royal & Ancient Golf Club (R&A) were asked to take control of the Rules. The first international set of Rules was then published in 1899.
The United States Golf Association (USGA) also adopted the R&A Rules and published them for American golfers in 1900. However the two golfing bodies then went their separate ways for the next 50 years.
As Barry states in the video, it is important to stress that there aren't two sets of Rules.