If you have ever seen two dogs when they meet, they greet each other face to face, unless there is a massive size disparity. So, why are we surprised when that is how a dog wants to greet us? You come home from work and let your dog out, and they are excited to see you and excited to show you how much they have missed you. So they jump up on you to get closer and give you some love. 
1. To assert dominance. Whether it's jumping on people or jumping on furniture, both instances illustrate a dog that wants to raise his station in life. By jumping on you or jumping on the couch, he's saying that he's the pack leader--something that you DON'T want to happen, as a dominant dog is much more difficult to train (and can become quite aggressive). In either case, you'll definitely want to institute the proper alpha dog training techniques, if you haven't already.
When your puppy reaches adolescence, he may be unable to control his impulses and start to test limits (just like a human child). Adolescent jumping up can turn into “nose boinking” which can lead to broken glasses or even a bloody nose. Jumping up often combines with mouthing behavior where the pup bites and grabs your hands, clothing or even your derriere in a grabbing game of tag.
If you have ever seen two dogs when they meet, they greet each other face to face, unless there is a massive size disparity. So, why are we surprised when that is how a dog wants to greet us? You come home from work and let your dog out, and they are excited to see you and excited to show you how much they have missed you. So they jump up on you to get closer and give you some love. 
If a dog is stressed or afraid, their demeanor and typical behaviors will change. If you see this in your dog (or really any dog you know) you should step back and check on your dog. Are they hurt? Did a new dog come around they don’t know? Has the weather changed? Is it hot outside? When was the last time they had a chance to go outside to pee or poop? 
A relatively new invention that will definitely solve this problem is the no jump harness. It works by restricting the movement of the dog’s hind legs so that it can’t jump at all. This should not be a permanent solution but rather something that can be effectively used during training. It should not only stop them from jumping chain link fences, but also from jumping on people and furniture.
Before you answer the door and welcome guests, clip a leash on your canine, preferably to a front-clip harness or head halter, so that he can be controlled in a manner such that he cannot greet if he jumps. When your dog is calm, with all four paws on the floor — which may take up to a few minutes for more excitable dogs — allow him to approach guests and say hello. If he jumps, gently turn and lead him away; wait for calm behavior before approaching again. For particularly excitable dogs, another option is to remove the dog to a contained area before guests come in. An exercise pen or baby gate is adequate containment for many dogs. If you have an athletic or large dog that can easily scale a gate, use a crate or move him to a room with a closed door. Once your dog calms down, clip on his leash and allow him to come out and greet your guests.
Why do dogs jump up? A plausible explanation arises from their ways of communicating with each other. A puppy greeting an adult dog often licks the adult’s muzzle -- a polite, deferential behavior. Dogs, of course, descend from wolves, among whom muzzle-licking is how pups get the grownups to regurgitate food for them. Domestic dogs rarely nourish puppies this way, but muzzle-licking has survived, maybe because deferential behaviors are handy for a social animal. Think of humans saying “No, after you.” Muzzle-licking is also an appeasement behavior -- something you trot out to de-escalate a fight. A human might lift up his hands, palms toward the person he’s arguing with.
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