Cinnamon (Cinnamomum verum, and three other related species) is the inner bark of a tree native to southeast Asia. Cinnamon was a rare and expensive spice in ancient times. It is mentioned in the Bible, and used by the ancient Egyptians. The origin of cinnamon was kept a secret for thousands of years, only being discovered by Western writers in the late 13th century. In the early 16th century, the breakdown of the traditional route the spice took to get to Europe was disrupted, which led the Portugese, Dutch, and English to explore the world for the source of cinnamon.
Cinnamon is produced by coppicing cinnamon trees that are two or three years old. The trees are cut off low to the ground during winter, and then sprout around a dozen shoots in the spring. These are cut when they reach a few inches in diameter, the outer bark is shaved off, then the stick is beaten to dislodge the inner bark, which is removed and allowed to dry. The cinnamon bark curls in on itself naturally, and is then cut into sticks that are a few inches long. The warm, radiant, spicy aroma of cinnamon comes from cinnamaldehyde.
Commercially, cinnamon is divided into four species, all in the genus of Cinnamomum. The four are: C. Verum, which comes from Sri Lanka, and is also called Ceylon cinnamon (the former name of Sri Lanka). Ceylon cinnamon is complex, not terribly "sweet", with a citrus and red-hot spicyness. C. burmannii, which is known as Korintje or Indonesian cinnamon is rounder and less sharp than Ceylon, with less citrus and more warmth of aroma. The third species is C. aromaticum, or Chinese cinnamon, which is also known as cassia. This species has higher levels of coumarin, which has a warm, vanilla-haylike aroma (and is also a liver toxin). Cassia is sharp and intensely hot-spicy, with a warm, buttery undertone. Finally, there is C. loureiroi, Vietnamese, or Saigon cinnamon. This is the powerhouse cinnamon - intensely radiant aromas, warm, rounded spicyness, and a lot of complexity.
In England and Mexico, Ceylon cinnamon is more common, but in the United States, Vietnamese is more prevalent. Cinnamon is used in cuisines all over the world. Vietnamese pho, Malaysian curries, the Moroccan chicken pie called b'stilla, Persian Sholeh Zard, oatmeal, cookies, and the classic cinnamon rolls all rely on the warm, radiant aroma and spicy flavor of cinnamon.
In cocktail usage, cinnamon is a part of many liqueurs, can be infused into simple syrup, and is a garnish, especially in warming winter drinks.