Cinnamon (Cinnamomum zeylanicum) is a small evergreen tree 10-15 m tall, belonging to the family Lauraceae, and a spice obtained from the inner bark of this species. It is native to Sri Lanka. The leaves are ovate-oblong in shape, 7-18 cm long. The flowers, which are arranged in panicles, have a greenish colour and a rather disagreeable odour. The fruit is a purple 1 cm berry containing a single seed.

Cinnamon is principally employed in cookery as a condiment and flavouring material, being largely used in the preparation of some kinds of chocolate and liqueurs. In medicine it acts like other volatile oils and once had a reputation as a "cure" for colds. The pungent taste and scent come from cinnamic aldehyde or cinnamaldehyde.

The best cinnamon is from Sri Lanka, but the tree is also grown at Tellicherry, in Java, Sumatra, the West Indies, Brazil, and Egypt. Sri Lanka cinnamon of fine quality is a very thin smooth bark, with a light-yellowish brown colour, a highly fragrant odour, and a peculiarly sweet, warm and pleasing aromatic taste. Its flavour is due to an aromatic oil which it contains to the extent of from 0.5 to 1%. This essential oil, as an article of commerce, is prepared by roughly pounding the bark, macerating it in sea-water, and then quickly distilling the whole. It is of a golden-yellow colour, with the peculiar odour of cinnamon and a very hot aromatic taste. It consists essentially of cinnamic aldehyde and, by the absorption of oxygen as it ages, darkens in colour and develops resinous compounds.

Cinnamon has been known from remote antiquity, and it was so highly prized among ancient nations that it was regarded as a present fit for monarchs and other great potentates. It is mentioned in Exodus 30: 23, where Moses is commanded to use both sweet cinnamon (Kinnamon) and cassia, and in Proverbs 7: 17-18, where the lover's bed is perfumed with myrrh, aloe and cinnamon. It is also alluded to by Herodotus and other classical writers.

Being a much more costly spice than cassia, that comparatively harsh-flavoured substance is frequently substituted for or added to it. The two barks when whole are easily enough distinguished, and their microscopic characteristics are also quite distinct. When powdered bark is treated with tincture of iodine (a test for starch), little effect is visible in the case of pure cinnamon of good quality, but when cassia is present a deep-blue tint is produced, the intensity of the coloration depending on the proportion of the cassia.

Culpepper's Herbal advises a daily draught of cinnamon in "any convenient liquor" against scurvy. Studies have found that using half a teaspoon of cinammon a day significantly reduces blood sugar levels in diabetics. The benefit, which can even be produced by soaking cinnamon in tea, also benefits non-diabetics who have blood sugar problem.