In many places throughout the world, horseshoes are nailed above the doorway or carried about as a lucky charm. There are a number of their supposed properties: -The horseshoe invokes the crescent moon or 'sacred vulva' shape of pagan moon goddesses (Artemis, Diana, etc.), and so invites their protection. -The (usually) seven nail holes in a horseshoe invoke the traditionally lucky number 7. -Horseshoes are usually iron, and iron repels fair-folk, keeping your house free of mischievous demons, imps, pixies, and elves. -Horseshoes are associated with blacksmiths, and smithing is considered a lucky profession. -A witch cannot walk under a horseshoe. -If the devil gets to close to a horseshoe, he will be sucked in. -A horseshoe in your bedroom will keep nightmares away. -Horseshoes can cure hiccups. In order to glean the benefits, there are rules, too: -The horseshoe must have been worn by a horse. -The horseshoe must have been found, not purchased. -(Mainly England/Ireland) The horseshoe must be placed facing up, or the luck will run out. -(Everywhere else) The horseshoe must be placed facing down so the luck can pour on you. As far as why they're thought to be lucky, there seem to be two factors: 1) They're roughly a crescent shape, which has been used as a protective amulet for centuries, and 2) They were once very common, and therefore an easy amulet for anyone to obtain. If you're going to imbue an object with magical properties, it might as well be one you can easily find! Related reading: http://www.luckymojo.com/horseshoe.html http://www.csicop.org/superstition/library/horse.html http://www.goodluckboutique.com/p_horseshoe.htm