Why does gravity work?

From a scientific viewpoint I mean. What is it that makes a smaller mass inexorably attracted to, pulled in, by something of a larger mass? I know, or I did when I took physics, the basics as to how we more easily stay on this planet, how the rotaion of earth cancels out all outward going vectors. But rotation forgotten for the moment, what is it that makes things close to a larger object be affected by it? Not even a smaller to a larger, but any two objects. What is the attraction between the two?