Eventing is an equestrian event which comprises dressage, cross-country and show jumping. This event has its roots as a comprehensive cavalry test requiring mastery of several types of riding. It has three main formats, the one day event (ODE), two day event and the three day event (3DE), which in reality now runs four days at some competitions. The sport was once referred to as "Militaire", and there is such a format that riders complete all three events in one day, called a "horse trial". Also, a "combined test" is a spin off of eventing which encompasses dressage and show jumping, but leaves out the cross country phase.

The Phases
Eventing is an equestrian triathlon, in that it combines three different disciplines in one competition set out over one day (one day event) or three days (three day event).
[edit] Dressage

The dressage phase at a 3-day.
The dressage phase (held first) comprises an exact sequence of movements ridden in an enclosed arena (20x60m for International 3DE but usually 20x40 for ODE). The test is judged by one or more judges who are looking for balance, rhythm and suppleness and most importantly, obedience of the horse and its harmony with the rider. The challenge is to demonstrate that a supremely fit horse, capable of completing the cross country phase on time, also has the training to perform in a graceful, relaxed and precise manner.
At the highest level of competition, the dressage test is roughly equivalent to the USDF Third Level, and may ask for half-pass at trot, shoulder-in, travers, collected, medium and extended gaits, single flying changes, and counter-canter. The tests may not ask for Grand Prix movements such as piaffe or passage.
Each movement in the test is scored on a scale from 0 to 10, with a score of "10" being the highest possible mark and with the total maximum score for the test varying depending on the level of competition and the number of movements. Therefore, if one movement is executed terribly, it is