(Quick Answer) Why Do Dogs Wag Their Tails?

To communicate and show how they're feeling at that specific moment, about the environment around them! A wagging tail can mean friendliness, happiness, excitement, and feeling good about something. To be more certain of how your dog is truly feeling, please make sure that you're looking at your dog's body language in its entirety. Ears, eyes, hair, body stiffness, mouth etc!