Most people think that if a dog is wagging his tail he is happy. While this can be a sign of happiness it can also mean many other things. Dogs use body language just as people do. A dogs tail can easily be compared to a human smile.

When a dog wags his tail it releases pheromones which are hormones produced by the anal glands. This is one way that dogs communicate their sex and social status to other dogs.
Which is why when two dogs meet they will often wag their tails while sniffing each others hind end. A fast wagging tail indicates that the dog is excited by something while a slower more relaxed wag is a sign that your dog is pleased and relaxed.

The alpha dog of a pack will hold their tails higher then the other dogs. So a good way to determine who is in charge is to see who holds their tail the highest. While a dog who is either fearful or submissive will tuck his tail between his legs and lower his head. This is his way of communicating to the other dogs that he is not a threat.

On the other hand a dog that is showing aggression will have a high, motionless and stiff tail and will hold his head higher, pin his ears and may show his teeth and growl but you will almost always see the first signs of aggression in the tail position. A dog that is alert will also have a motionless and stiffened tail position.

Besides the communication factor, dogs also use their tails for balance. A good example would be the long tail of a greyhound. Greyhounds actually use their tails as a kind of rudder when they are running.

Your dogs tail is as important to them as our voices are to us. If you really want to know what your dog is thinking you must pay attention to these subtle displays and twitches of the tail. While the tail is not the end all to a dogs communication it is always one of the easiest to recognize. Our dogs are always trying to communicate with us but we often times completely ignore or misread what they are saying. Next time you are with your dog pay more attention to his tail and you may learn more about his personality than you ever thought possible.