Eventing is an equestrian triathlon, in that it combines three different disciplines in one competition set out over one, two, or three days, depending on the length of courses and number of entries. This sport follows a similar format in Australia, Canada, Ireland, United Kingdom and the United States

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Eventing (also known as three day eventing or horse trials) is an equestrian event where a single horse and rider combine and compete against other competitors across the three disciplines of dressage, cross-country, and show jumping. This event has its roots in a comprehensive cavalry test that required mastery of several types of riding. The competition may be run as a one-day event (ODE), where all three events are completed in one day (dressage, followed by show jumping and then the cross-country phase) or a three-day event (3DE), which is more commonly now run over four days, with dressage on the first two days, followed by cross-country the next day and then show jumping in reverse order on the final day.