There are some slight differences in the rules used in different countries around the world, however for almost all practical purposes (more than 99.999% of games) they produce the same result. A narrative description of the differences is here.
We have adopted American Go Association-style rules for use in tournaments, as opposed to Japanese rules previously. Please see our policy page Rules of Go for the full details.
For a comparison between the various rules sets see our Rules Comparison page.
Some other sites which also present the rules of Go in English, not in a formal way, include:
Which of these you like is primarily a stylistic issue.
Ko is the main repeating position for which there is a specific rule to avoid the game going on forever. However, there are more complicated, and usually fairly rare positions which are repeating and for which special rules are needed to find a conclusion for a game. Some of these can be seen here. The rules related to these differ between the major rule sets.
For links to rule sites in foreign languages see our Foreign Links page.
The Rules of General Graph Go are how a mathematician may see Go.