Okay let me make this short and simple… I am a Show Jumper and I will be getting a new horse. The reason I am getting a new horse is because I am in need of a more trained horse that can run faster, jump higher, and do dressage. I am trained a little in Dressage and a lot in Show Jumping. I have grown tired of Jumping and now I want to move on to eventing. Here are some questions I want to ask…
What do the judges look for?
What tack do I use?
There is a stubben eventing saddle and a Amerigo eventing saddle. What do you do?
How can I find an eventing instructor?
Is this sport fun?
Is this sport hard compared to jumping?
What horse breed is most common?
Will the judges like my Arabian if that is the horse breed I choose to go with?
What kind of things should I be looking for in a eventing horse?
Thank you in advance! If there is anything more you would wish to tell my I would love to hear it 
I don’t compete in eventing, but primarily because I can’t afford a horse right now. It’s the sport I intend to compete in when I have a horse.
As far as what judges look for; just like in regular dressage, judges want clean movements executed with a minimal cue. In cross country, you just want to get over the fences fast and clean, but you want your horse’s stamina to last. You’re only marked down or disqualified if you fall off, your horse falls, or your horse refuses a fence. Cross country is judged on time – you want to get done as close to the allotted time as possible. Show jumping is just like normal show jumping. Errors earn you penalty points – the least penalties earned wins.
For tack, you want saddles for all three events if possible, but for the very lowest levels, one all-purpose saddle can work, and beyond that you can get by with a dressage saddle and a close contact saddle (to be used for both cross country and show jumping). I’m not sure about bit requirements and so on – I’d suggest looking at the United States Eventing Association site and seeing if they have the rulebook posted (or whatever the association for your country might be). I wouldn’t buy an eventing saddle until you’re sure you like it, and you want to get to higher levels.
For an eventing instructor, I would suggest you talk to your show jumping instructor, or find someone who does jumping and dressage. Call people in your area and see if you can get someone’s name. Again, the eventing association might be able to help; many associations have directories of trainers.
Fun? Having not gotten the chance to do it yet, I can’t say for sure, but it looks like fun to me!
Most of eventing is jumping; you do dressage first day, cross country second, show jumping third (at higher levels…for low levels you’d do all three in one day or you’d do dressage and show jumping day one and cross country day two). However, you need the stamina to ride over a course of very sturdy jumps for cross country. The levels used for eventing aren’t the same as levels used for dressage or show jumping – Grand Prix show jumping is higher than CCI**** show jumping fences. I don’t know of the exact level correlations though, although I’m trying to get that figured out. Visit http://equinerevolution.cwahi.net in a month or so and I’ll hopefully have it in the library.
Thoroughbreds tend to be the most common in the breed, but it’s definitely not exclusive to them; Teddy O’Connor competed at the highest levels and he was part Shetland Pony. Unlike many sports in the equine world, there’s no bias based on breed; however, Thoroughbreds tend to dominate because they’re really the only breed who have the strength and stamina to gallop several miles and jump fences, and then go through show jumping the day after.
What you want in an eventing horse: they have to be disciplined and quiet enough to handle dressage, but they need the strength and stamina to handle cross country (they’ve got to be able to gallop 3-4 miles), and have the speed to make it over a jumping course. They’ve got to be sound. If you can get a Thoroughbred with the X factor (which gives an enlarged heart) that’s a bonus. Off-track Thoroughbreds are really popular, because they have a lot of the qualities to compete at the upper levels (although many breeds compete at the lower levels).
An instructor could tell you a lot more than I could, but that’s a bit of what I know.
If you want to try it virtually, I HIGHLY recommend the game "Equestriad 2001" if you can find it. I think it was really overlooked, but it has the Rolex, Badminton, and Burghley courses as well as the 2000 Olympic course, along with a bunch of famous horses and riders (though I like to make my own!). Most English-riding oriented games will feature eventing, although each element might be separate.