Sixteen teams will compete in the 2021 World Cup, the Rugby League International Federation has announced.
Organisers will turn the clock back to 2000 when the teams were divided into four groups of four, with the top two from each going through to the knock-out stages.
That was generally regarded as a failure, as it produced a series of one-sided group matches, and when the World Cup was next held, in 2008, the number of participants was cut to just 10.
The number went up to 14 for the successful 2013 World Cup and will stay there for the 2017 tournament but it is a sign of the increasing confidence in international rugby league that the organisers have pushed it back to 16.
"The growth of rugby league internationally is reflected in the expansion of the tournament to four pools of four," RLIF chief executive David Collier said.
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"The strength of the 2017 World Cup qualifiers to date, across the continents, has shown a significant increase in playing standard and quality and the newly-adopted international calendar will ensure that teams will have a minimum of 15 months prior to the 2021 event to stake their claim."
In addition, the 2021 Women's World Cup, which will run at the same time, will be increased to six nations.
Collier added: "The World Cup is the pinnacle and we are already receiving expressions of interest to run the 2021 events in world-class facilities to provide the players and supporters with the highest possible experience.
"Bids are due to be returned to the RLIF by the end of June - we are anticipating and encouraging more nations to apply - and the hosts will be announced by the end of 2016."
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