Why Dogs Bark

Source: 

The Humane Society of the United States

Dogs have a lot to say, and they do it by barking. They bark to go out, come in, to tell you a stranger's in your yard, and at people, cars, and other animals. Too much barking or barking at inappropriate times can be a problem. You want to be respectful of your neighbors as well as local laws, so you need to get your dog's barking under control.