First as scavengers, later as companions, helpers, and protectors, dogs have been with us a very long time. Forty percent of U.S. households have at least one dog, according to the American Pet Products Manufacturers Association--even though dogs are now outnumbered by cats.

For most of us, pets are part of the family. But in a crowded modern world, the law doesn't always treat them that way. More and more laws regulate when dogs must be leashed or confined, where their owners may take them, and even how many may live in a house. And while dogs used to get "one free bite" before their owners were liable for injuries they caused, that's no longer true in most states.