History
The annual Champions Trophy tournament is field hockey's version of a world championship. The men's event began in 1978. After skipping a year to 1980, it's been annual ever since. The women's tournament was inaugurated in 1987 and was held every two years until 1999, when it became annual.
Six teams qualify for each tournament. In the year following a World Cup or an Olympics, the six teams include the host, the defending champion, the World Cup or Olyimpic champion, and the next highest ranked teams, excluding those already qualified, from either the World Cup or the Olympic Games.
The following year, the team that finished last is replaced by the winner of the Champions Challenge.
In odd-numbered years, the Champions Challenge tournament is held to pick that sixth team. There are also six tams in the challenge event, the pre-selected host and the five top ranked World Cup or Olympic teams that haven't already qualified for the Champions Trophy.