IAAF World Cross Country Championships is the most important competition in international Cross country running. Held annually and organised by International Association of Athletics Federations, it was inaugurated in 1973, when it replaced the International Cross Country Championships.

Traditionally, the World Cross Country Championships consisted of four races: one each for men (12km) and for women (8km); and one each for junior men (8km) and for junior women (6km). Scoring was done for individuals and for national teams. In the team competition, the finishing positions of the top six scorers from a team of up to nine are summed for the men and women, respectively, and the low score wins. For the junior races, the top three from a team of up to four are scored.

The year 1998 saw the introduction of two new events at the World Cross Country Championships, a short race for men and a short race for women. The last time these 4km races were held was 2006, and there are no public plans to bring them back.

In an incredible show of dominance, the senior men's team race has been won by Ethiopia or Kenya every year since 1981 in both the short and long races. These nations have enjoyed a similar strangle-hold on the junior men's races since 1982. In the senior men's 12km race, Kenya won the world championships for an astounding 18 years in a row, from 1986 through 2003, a record of unequaled international success. Likewise on the women's side, only one other nation has won the long team race since 1991: Portugal, in 1994. These African nations were not quite so dominant in the short races, but they have won every women's junior race since its introduction in 1989.

Several athletes have won three or more individual titles: Carlos Lopes, the first man to win three times; John Ngugi, the first man to win five times; Paul Tergat, the first man to win five times in a row; Kenenisa Bekele, the only man to win the short and long courses each five times in five years; Grete Waitz, the first woman to win five times (although Doris Brown Heritage won the International Cross Country Championships five times between 1967 and 1971); Lynn Jennings, who won three times; Derartu Tulu, who won three times; Gete Wami and Tirunesh Dibaba, both of whom won twice at the long course and once at the short; and Edith Masai, who won the short race three times. Tirunesh Dibaba was also once the junior women's champion.

Many consider the World Cross Country Championships to be the most difficult races to win, even more difficult than the Olympic Games. At most major championships, the world's best distance runners are separated into a few races, i.e. 3000m Steeplechase, 5000m, and 10,000m. However, in the absence of the short course races, the World Cross Country Championships pit all runners against one another in only one race. Thus, the competition is quite fierce. It's no wonder, then, that several Olympic Champions have gotten their start as World Cross Country Champions: Carlos Lopes, marathon, 1984; John Ngugi, 5000m, 1988; Khalid Skah, 10,000m, 1992; and Kenenisa Bekele, 10,000m, 2004. Numerous other champions have medalled at the Olympic Games or the World Championships, or have set World Records.