Greater Swiss Mountain Dogs
Breed Information
Here is the AKC breed standard for the Greater Swiss Mountain Dog (aka Swissy)
All of the above are great links that should give you a lot of basic information, here are just a couple of additional things we would like to add from our personal experience:

If you are looking for an 'easy' dog that you can just put out in the backyard and bring in every once in a while, then the swissy is probably not right for you. Adult swissies that have been well-socialized and taught proper manners are typically very sweet, loving, and make great pets. These are the type of dogs that everyone sees or hears about and thinks they want a Swissy because of them. These dogs didn't end up that way by magic though.
As puppies, swisses are very hard to housetrain, they tend to eat and/or chew things they aren't supposed to, they require a lot of early socialization, and they require a lot of firm, consistent training. Some swissies will constantly test you to see who is going to be the leader of the house (especially for the first 2 years), you will need to make sure you understand how to train a large, intelligent, stubborn dog.
Swissies need a lot of socialization, constant socialization throughout their life, but especially as puppies!
Swissies were bred to be an all-purpose farm dog, they were supposed to watch out for things that were out of the ordinary and if you don't spend time when they are young exposing them to tons of different situations and people, then they will think that these things are meant to be 'warned' about and will be hesitant and vocal when exposed to new things.
Yes, swissies shed! Depending upon how much undercoat they have it can be a lot of hair! You will be sweeping your house constantly, they can be messy drinkers, and although they are a dry-mouthed breed they still will leave water all over your floor. Plus, as puppies they can pee HUGE puddles and the boys are notorious for walking while they pee so that they leave a trail from one end of the house to the other. If you aren't ready to be cleaning up puppy pee multiple times a day then don't purchase a swissy puppy. No matter how many puppies you have raised, a swissy puppy will prove to be a tough housebreaker - prepare yourself in advance!

Pretty much all swissies bark, some more than others. Ours are generally quiet until they see or hear a weird noise. Swissies need to feel like they are part of the family, they do not make good outdoor dogs (and they HATE the heat!). We will not sell a puppy to anyone who plans to keep their dog outside, we don't feel like this is a good situation for the puppy to grow up in, and if all you want is an outdoor watch-dog, there are several breeds that are much better suited for the task.
Swissies can be great dogs, but it definately takes a lot of work to get them that way. The first time many people meet their first Greater Swiss Mountain Dog they are impressed by their sweet demeanor and stunning good looks, but keep in mind that the reason you probably met them is because their people were devoted to socializing them and making sure they were out exercising and meeting new people all the time! Swissies love to have a job, just because they aren't your typical obedience type breed doesn't mean they don't like to work, you just have to be creative in finding the things they like to do best.
Please feel free to contact us with any additional questions or comments, or to set-up a time to meet any of our dogs in person!