2025 FIVB Volleyball Men's U21 World Championship

The 2025 FIVB Volleyball Men's U21 World Championship will be the 23rd edition of the FIVB Volleyball Men's U21 World Championship, contested by the men's national teams under the age of 21 of the members of the Fédération Internationale de Volleyball (FIVB), the sport's global governing body. It will be held in August–September 2025 in a host nation to be determined.

Starting with this edition, the tournament will be expanded to include 24 teams instead of the 16 teams of previous editions, following the decision adopted by FIVB in June 2023.

Iran are the defending champions.

Competition formula changes
In June 2023 during a three-day meeting in Punta Cana, Dominican Republic, the FIVB Board of Administration approved the proposal made by its Volleyball Council to increase the number of participating teams to 24 in its Age Group World Championships (U19 and U21 in both genders). Consequently, the distribution of quotas by confederation for the Women's U21 World Championship was modified regarding previous editions, ensuring one automatic quota for the defending champion and assigning two quotas based on the corresponding FIVB Age Group World Ranking.

The new competition formula was in line with the one adopted for the 2023 FIVB Volleyball Boys' U19 World Championship, which was also contested by 24 teams.

Host selection
On 28 March 2024, FIVB opened the bidding process for member associations whose countries were interested in hosting one of the four Age Group World Championships in 2025 (i.e., U19 Boys' and Girls' World Championships and U21 Men's and Women's World Championships). The expression of interest of the member associations had to be submitted to FIVB by 30 April 2024, 18:00 CEST (UTC+2).

Qualification
A total of 24 national teams will qualify for the final tournament. In addition to the host team and the defending champions who qualified automatically, 20 other teams will qualify through five separate continental competitions which were required to be held no later than 31 December 2024. Two remaining teams will enter the tournament via the Men's U21 FIVB World Ranking (as of 31 December 2024) among the teams not yet qualified.

The slot allocation per confederation was set as follows:
 * Defending champion (Iran): 1
 * AVC (Asia & Oceania): 4
 * CAVB (Africa): 3
 * CEV (Europe): 6
 * CSV (South America): 3
 * NORCECA (North, Central America and Caribbean): 4
 * Host: 1
 * Top teams not yet qualified as per Men's U21 FIVB World Ranking: 2