The horse (Equus caballus) evolved in North America for millions of years. Then, around twenty thousand years ago — a blip in evolutionary time — the species seemingly disappeared from the continent. Now, the horse has returned to North America in vast numbers, in both domestic and wild herds. Wild horses are now protected by federal law, but a debate rages on among ecologists, animal welfare advocates, and ranchers about what the horse’s role in the natural landscape should be. Each year, thousands of wild horses are rounded up and sent to holding facilities, where some are adopted to loving homes, while many others end up in a slaughter house. El Caballo documents one of the most complex wildlife management issues today. What should the human relationship with wildlife be, and what constitutes a native species? Finally, where do modern wild horses fit in our view of the natural world?