A farrier is a specialist in fitting shoes to horses, and sometimes other hooved animals as well. Nowadays, farriers are not as widespread as they once were, due to a decline in the use of horses as work animals, but they are still highly respected, because their work requires skill with both horses and metals. Many farriers work in rural areas, and people who are interested in farriery as a career can attend courses at schools which train farriers.
As you probably already know, shoes are an important piece of equipment for domestic horses. A basic pleasure horse requires a fairly simple set of shoes, but where farriers can really demonstrate their abilities is by providing shoes to correct gaits, increase traction for sport horses, and to correct medical conditions like laminitis, among other things. Corrective shoeing can be a very lucrative branch of farriery, as it can turn an unusable horse into a reliable, healthy mount. Some farriers may choose to specialize in a specific type of shoeing, such as shoeing racehorses, jumpers, or gaited horses, and such a farrier may be in high demand.
At a farrier school, people learn about horses, metalworking, and how to recommend and fit shoes. A farrier must be comfortable around horses, and able to handle animals with a wide range of manners, from gentle ponies to high strung racehorses. Farriers also learn about anatomy and physiology, and the myriad problems which can injure the legs and feet of horses. Many of these conditions are preventable or treatable with corrective shoeing.
Horseshoes must be uniquely fitted to each animal. So, farriers learn to shape metal, using either cold shoeing, where the shoes are beaten into shape while the metal is cold, or hot shoeing, where the shoes are worked in a forge. Improperly fitted shoes can severely injure a horse, and as a result it is very important to find a qualified, skilled farrier to shoe your horses. Some farriers belong to national organizations with basic membership requirements, and you can also ask other horse people in your area about the best choice of farrier for your horse.