List of 125cc/Moto3 World Riders' Champions

Grand Prix motorcycle racing is the premier championship of motorcycle road racing, which has been divided into three classes: MotoGP, Moto2, and Moto3. Former classes that have been discontinued include 350cc, 250cc, 125cc, 50cc/80cc, MotoE, and Sidecar. Moto3 replaced the 125cc class in 2012. Moto3 runs 250cc single-cylinder engines as opposed to the 125cc engines used previously. The engines have single cylinders, as opposed to the four cylinders used in MotoGP. Moto3 is the class where young riders first participate in Grand Prix motorcycle racing. The minimum age for a rider is 16 years and the maximum is 28 years. However, after a rash of incidents involving young rider fatalities in lower classes, the FIM set a minimum age of 18 starting in the 2023 season. The Grand Prix Road-Racing World Championship was established in 1949 by the sport's governing body, the Fédération Internationale de Motocyclisme (FIM), and is the oldest motorsport world championship.

Points earned in these events count toward the drivers' and constructors' world championships. The driver's and constructor's championship are separate championships, but are based on the same point system. The number of points awarded at the end of each race to the top 15 qualifying riders depends on their placement. Points received by each finisher, from first 1st place to 15th place: 25, 20, 16, 13, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. Historically, there have been several points systems. Results from all current Grands Prix count towards the championships; in the past, only a certain number of results were counted.

Ángel Nieto has won the most championships, with seven. Loris Capirossi is the youngest to win the championship; he was 17 years and 165 days old when he won in 1990. Spanish riders have won the most championships; 18 riders have won a total of 24 championships. Italian riders have won the second most; 15 riders have won a total of 24 championships. Riders from Great Britain have won the third most, as five riders have won a total of five championships. Nello Pagani won the inaugural championship in 1949. Nicolas Terol was the last rider to win the 125cc championship in 2011. Rupert Hollaus' 1954 title was the only time a posthumous World Champion was crowned in any class in Grand Prix motorcycle racing as he was killed before the 1954 season was over. Emilio Alzamora was the second rider in history to win a Grand Prix motorcycle world championship without having won a race in 1999 after Manuel Herreros. Sandro Cortese was the first rider to win the Moto3 championship in 2012. José Antonio Rueda is the current champion; he won the 2025 Moto3 World Championship.