When dogs lick each other's face, they're not exactly kissing. It can be a sign of affection, but more likely, it's a sign the licker wants to play or is busy setting the social order. Licking is the opposite of aggressive behavior, so get ready to enjoy some play.
Whether dogs are meeting for the first time or already best buds, licking each other's mouth is often a sign they are ready to play. It's often combined with a wiggly booty and lowered front legs, signifying a desperate need to engage in something fun. If the dog being licked isn't in the mood for play, it's best to move the other pooch away before the licking can become obsessive; the other dog finds non-stop licking just as annoying as you do.
Dogs can get frustrated with each other, especially if one is more high-energy. The offending pooch can say she's sorry with a gentle face lick. She usually comes in from below and licks the other dog's mouth, and she might raise a paw slightly, says the ASPCA. When the other dogs licks back, all is forgiven.
Social order is important in dog life. You should be the alpha dog, but they'll create their own pecking order under your umbrella. Licking is often a sign of submission. A dog lower down the chain might greet one higher up the chain by licking her on the mouth. She also might roll over onto her back to express her submissiveness. Keep an eye on dogs when one is submissively licking; the dominant dog might get overexuberant and growl or snap at the submissive one.
Puppies seem to stay hungry; they're growing so fast that they need lots of nourishment. One way they tell grown dogs how they're feeling is by licking them on the mouth. The big dog isn't likely to feed the puppy -- that's your job -- but the puppy doesn't necessarily know that. Instinctively, she thinks it's the adult dog's job to find food and bring it back for her to eat. This could translate into why the puppy is licking you on the face -- although she could just be giving you love.