FIFA has voted to expand the football World Cup to 48 teams from its current 32, brushing aside concerns it would lower the overall standard of the tournament, and make it too big and unwieldy.
The sports governing body said its decision-making panel voted unanimously in favour of the change, which will be introduced at the 2026 tournament.
FIFA president Gianni Infantino, who replaced the disgraced Sepp Blatter in February, had made World Cup expansion one of his promises during his successful electoral campaign.
Infantino had initially suggested a 40-team tournament but then added another eight to that total in October.
FIFA's 211 member associations each hold one vote in the presidential election and 135 of them have never played at a World Cup, so expansion of the tournament was always likely to appeal.
Those who have never qualified include 41 out of 54 of its African members and 10 out of 11 members in the Oceania region.
Infantino said the move meant that "more can participate and many more will have a chance to dream".
The new format will feature a first round of 16 groups of three teams, with the top two in each qualifying for a round of 32.
From then on, it would be a straightforward knockout contest.
The hosts of the 2026 tournament will be decided in May 2020.
The CONCACAF Confederation, representing North and Central America and the Caribbean, is seen as a strong contender, possibly providing a joint bid from at least two of the United States, Canada and Mexico.
The new-look tournament will increase the number of matches from 64 to 80, but Infantino said it would require the same number of match days and stadiums as now:
"This format can be played in exactly the same number of days as today, 32, and the winning team will play the same number of games, seven, as today, and in the same number of stadiums, 12, as today," he said.
Critics have said that FIFA is tampering with a winning formula; the last World Cup in Brazil was widely regarded as one of the best in the competition's 87-year-old history, featuring shock results, last-minute drama and outstanding individual performances.
One of the concerns is that the new format will make the group stage merely a matter of avoiding elimination, and so encourage negative play.
Infantino said it had not yet been decided whether penalty shootouts could be used to decide drawn group-stage matches.
The qualifying competition, meanwhile, is likely to become a mere formality for many of the strongest teams.
The number of extra slots for each continental confederation, as well as formats for the qualifying competitions, will be decided at a later date, Infantino said.
Those who have never qualified include 41 out of FIFA's 54 of its African members and 10 out of 11 members in the Oceania region.
The ECA, the association that represents more than 200 European clubs, most of which dislike releasing their players for international duty, said the decision had been taken for "political reasons rather than sporting ones" and "under considerable political pressure".
"We fail to see the merits to changing the current format of 32 that has proven to be the perfect formula from all perspectives," it said in a statement.
Reinhard Grindel, head of the German federation (DFB), said he saw a danger that "in the future we will see more defensive-minded teams".
"If the World Cup stops being as attractive, then fan and sponsor support suffers, as does its marketing."
The pressure group New FIFA Now, which has campaigned for reform of FIFA, said the move "will make a mockery of the qualification process for most confederations".
The inaugural World Cup in Uruguay featured just 13 teams and 18 matches.
Sixteen teams took part from 1934, eight more were added from 1982 onwards and, finally, another eight in 1998.