The International Rugby Board (IRB) has decided that 20 teams will compete at the 2011 World Cup in New Zealand.
South Africa beat England to win the 2007 World Cup final in Paris
There had been suggestions before this year's event that only 16 teams would be allowed to play in four years' time.
There were concerns smaller nations would be uncompetitive in France, but their performances allayed these fears.
IRB chairman Dr Syd Millar said: "The developing nations at Rugby World Cup 2007 have produced significantly enhanced performances since RWC 2003."
The 2007 World Cup was won by South Africa, who beat England 15-6 in the final, but some of the most impressive performances came from teams previously considered to be 'minnows' in the world game.
Fiji defeated Wales to reach the last eight and were level at 20-20 with South Africa after an hour of their quarter-final, while Georgia came within four points of defeating Ireland in their pool game.
A further change means there will be 12 automatic qualifiers for 2011, rather than eight as has previously been the case.
That means both Wales and Ireland are guaranteed their places in New Zealand despite finishing third in their pools in France.
Tonga and Italy also join the automatic qualifiers, who include both England and Scotland.
Meanwhile, the IRB is set for further discussions over plans to introduce a so-called "world series" in an attempt to strengthen Test rugby.
Under the plan matches between the Six Nations and Tri-Nations teams, plus Argentina, would count towards an annual league ending in a Grand Final.
It is one of two options, along with a 12-team competition taking place over two years between World Cups, which came out of the IRB forum on the game's future this week.
The IRB said the delegates had asked the governing body to "further explore" the two possibilities.
Other points to have come out of the forum include:
Players guaranteed a minimum of 10 weeks' post-season rest
Test matches limited to 11 per year
English and French professional club seasons to finish by 31 May
Argentina to be fully integrated into international calendar over four-year period starting from 2008
Further investment and new competitions for emerging nations
A permanent Rugby World Cup window of September-October
The forum also agreed that Argentina's future lies in the southern hemisphere, ruling out the possibility of the Pumas, who finished third at the World Cup, joining the Six Nations.