The Masuda Method

  The Madsuda Method, named after Game Freak director Junichi Masuda, is a method of hatching shiny Pokemon from eggs more easily.
  This trick has been implemented is Generations 4 and up. In Generations 4 this increases the chances of hatching a shiny to 1/1638. In Generation 5 games, this increases the chances to 1/1365. it is unknown what the exact percentages are for Generation 6 games, but they have been increased even further.
  This trick can be performed by breeding two Pokemon of different nationalities, of which can be received via GTS and Wonder Trade.
  Below is a graphic that displays The Masuda Method at work.

Parents		Offspring
Two Pokémon from the same country
Onix ♂	Steelix ♀	Onix
Two Pokémon from two countries
Glalie ♂	ユキメノコ ♀	Snorunt
Breeding with an in-game trade
Gyarados ♂	Foppa ♀	Magikarp