Humans and horses have a long, interrelated history, yet no one is truly certain when and where horses were first domesticated and ridden. We do know, however, that the first horses had toes, not hooves, and looked nothing like the horses of today. This chapter highlights the current facts known about the early ancestors of the modern-day horse and its evolution. It also covers the ways in which the horse helped advance human civilization, from conquering foreign lands in battle to plowing and settling new frontiers.