Do you know that capers are actually flower buds? They grow on a trailing shrub native to the Mediterranean region. Capers are harvested in the spring and early summer when the buds are still tightly closed; they're then dried in the sun and pickled. The delicate, salty buds are a key element of Mediterranean cooking. The size of capers varies; the smaller, most-common kind are called nonpareils. When you buy capers, they will be packed either in salt or brine. If they're packed in brine, drain them before use and rinse, if desired, to remove some of the saltiness. Salt-packed capers should be soaked for about 15 minutes and rinsed.
Caperberries grow on the same bush as capers, appearing after the buds have bloomed. You'll find these in stores cured in brine -- they are a nice alternative to olives for martinis.