Americans like to own their homes, and the rules and conventions for ownership are generally well understood. So it's easy to forget that in many corners of the globe the rules are more ambiguous--and more open to challenge. Indeed, there are an estimated one billion squatters in the world today--people who, mostly out of necessity, are living on property they do not own and cannot afford. Squatters rarely have a voice, but in a few industrialized cities where they do, their claims are usually founded on the idea of improvement. If an owner abandons or neglects a property, shouldn't another human being be allowed to take shelter, invest sweat equity in making it a home, and lay some claim to it? In other words, does hard work improving a property convey some right to occupancy, even ownership?