Ema are small wooden plaques on which Shinto worshipers write their prayers or wishes. The ema are then left hanging up at the shrine, where the gods receive them. They tend to be fairly uniform in size and shape, but many have different pictures painted on them, of animals or other Shinto imagery, and they often have the word gan'i (wish), written along the side. They are for many purposes depending on the shrine or the type one buys. The most common reasons for buying a plaque is for annual success, success on exams, marital bliss, to have children, and to avoid of illness (for health). Some shrines specialize in certain types of these plaques, and usually offer a variety at the larger shrines. Nominally these are akin to supporting the shrine financially as all shrines must be independent of government funding. This is just one of the types of charms available at a shrine.
At some of the more central and popular shrines, such as Meiji Shrine in Tokyo, one can find ema in many languages, as tourists leave their own wishes and prayers.