The qualification structure was as follows: First round (group stage): The 54 teams were divided into nine groups of six teams each to play home-and-away round-robin matches. The winners of each group qualified for the 2018 FIFA World Cup, and the eight best runners-up advanced to the second round (play-offs).
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Third round: The 12 teams (an increase from 10 for 2014) which advanced from the second round were divided into two groups of six teams to play home-and-away round-robin matches. The top two teams of each group qualified for the 2018 FIFA World Cup, and the two third-placed teams advanced to the fourth round.