The cross-country course is approximately two and three quarter to four miles (6 km) long, comprising some twenty-four to thirty-six fixed and solid obstacles. Obstacles usually are built to look "natural" (out of logs, for instance), however odd materials and decorations may be added to test the horse's bravery. Obstacles can include all those that might be found if riding across the countryside, including water, trees, logs, ditches, and banks.

All obstacles or compulsory passageways are flagged, with a red flag on the right and a white flag on the left. A black stripe on the red flag indicates that it is an option for the obstacle, and another route may be taken if the rider so chooses, without penalty. All obstacles are numbered, and the color of the numbering can indicate which level the fence is for if multiple levels are competing at the event. (for example, white numbers on a green background indicate that the fence is on the Preliminary level course, however, in British eventing, this color combination would indicate the intermediate track, so riders should always check the course map for course markers).

Cross-country courses for eventing are held outdoors through fields and wooded areas. The terrain is unique for each course, which usually incorporates the course into the natural terrain of the area, and therefore events in certain parts of the world may be held on mostly flat land, while others are over very strenuous hills.

Good course designers will use the terrain to either help the inexperienced horse and rider at the lower levels to prepare for an obstacle, or to make an obstacle more difficult for the experienced competitors. For example, the designer may place a fence at the opening of a wooded area, resulting in a lighting difference between the takeoff and landing side. This requires careful riding and a confident horse. Designers may make an obstacle more difficult by placing it along the side of a steep hill, at the top of a mound (so the horse can not see the landing until he is about to take off, testing bravery), or use the natural trees and ditches to force riders to take slightly more difficult lines to their fences.

A good course designer will be able to incorporate the obstacles into the landscape so that they seem natural, yet still fairly test the horse and provide the horse an option to run-out if the rider makes a mistake. Most designers use accuracy fences, such as skinnies (fences with a narrow face) and corners, to make the rider's job more difficult, while still being very "horse-friendly."

All courses begin with a "start box," where the horse and rider wait as the time keeper begins to count-down to their start time. They are not allowed to go out the front of the box before the timer reaches zero on the count-down, nor are they allowed to have a flying start. The first few fences of most well-designed courses are usually straightforward and inviting, such as a large log or roll-top, which helps to build the horse and rider's confidence, get them settled in a galloping rhythm, and beginning to focus on the job at hand. The technicality of the obstacles then begins to increase, and elements such as banks, ditches, and water are introduced. The final fences of a course are usually slightly easier, to allow the horse and rider to finish on a good note, before they gallop across the finish.

Good footing is very important to most riders, as it helps decrease the wear-and-tear the sport has on their horses and avoid injury that may occur due to deep or slippery ground. The rider should always take care to note the footing while walking the course, and adjust the planned route to avoid patches that are especially boggy, slippery, or rough, and to avoid holes that may be present.

Footing is never used to make a course more difficult (for example, a fence is never purposely placed in a boggy area or one with sharp rocks). Instead, most competitions go out of their way to keep the footing safe, and many of the larger events may "groom" the footing to get it to the appropriate firmness.

Riders walk a cross-country course, usually between 1-3 times, before they actually ride it. This allows them to evaluate the course and determine how each jump needs to be ridden.

All horses are started with distance work, at a slow speed (usually a walk or trot), to improve endurance. This "base" of fitness is vital to ensure the horse is physically sound enough to progress to more rigorous work, such as galloping. Horses who do not have a base are much more at risk for soft tissue injury. After a base has been placed on the horse, riders add in galloping sets to improve cardiovascular fitness. Most riders use interval training, in which the heart rate is raised to a certain level before the horse is allowed a rest, and then the horse is again asked to work before the heart has a chance to fully recover. This can improve the cardiovascular fitness of the horse with less overall galloping, helping to maintain the horse's soundness.

Work up an incline (hill work) is often favored over longer stretches of galloping for improving fitness, because it requires the horse to work harder while placing less wear-and-tear on their body. Through experience, a rider may gauge the difficulty of a hill and determine what its comparative worth is to galloping on a flat surface.

To condition the horse's bones, riders may walk on roads or other hard surfaces. However, this is generally only used when the ground conditions are quite soft. Although popular in Britain, most American riders do not do road work. If used too much, it can encourage arthritis.

Some riders also have access to equine treadmills or swimming pools. Treadmills can sometimes be adjusted to have a slight incline, allowing the horse to work without the added weight of the rider. Swimming is an excellent form of conditioning, and allows the rider to increase the horse's cardiovascular and muscular condition without adding undue stress to the bones or soft tissue.

Riders should always be wary of the ground conditions. Conditioning on hard ground can cause lameness problems, both short and long-term. Conditioning on deep, heavy footing (such as right after a rain) increases the pull on the tendons, and may lead to soft tissue damage. Conditioning on slippery ground increases the risk that the horse will slip and have a soft-tissue injury. In general, older horses do better on softer footing, which is kinder to any joint problems they may have. Younger horses, which may not have the same strength of soft tissue, are best worked on slightly firmer ground.

The rider should also take care to slowly increase the amount of work. As a general rule, the distance may be increased or the speed may be increased, but not both at once. Pushing a horse too fast can lead to injury or lameness. The rider should also be aware of the horse's breathing, and feel how tired the animal is underneath. Horses conditioning for the upper levels are often conditioned with heart rate monitors, so the rider will have a great insight into the horse's condition over time.

The rider should always be willing to cut back conditioning work if the horse feels exhausted or if he has a very high respiration rate. Heat and humidity make work much harder, so should be considered while conditioning. Horses that are pushed too hard may injure themselves or may overheat, which can be deadly if not correctly cared for.

The rider must also understand that the muscling and improved cardiovascular fitness that is seen within a month or two of conditioning work does not indicate that the horse's entire body is at the same peak. Soft tissue can take several months to condition, and bone, up to a year.