Cinnamon (Cinnamomum cassia) is the brown bark of the cinnamon tree, which when dried, rolls into a tubular form known as a quill. Cinnamon is available in either its whole quill form (cinnamon sticks) or as ground powder.

While there are approximately one hundred varieties of Cinnamonum verum (the scientific name for cinnamon), Cinnamonum zeylanicum (Ceylon cinnamon) and Cinnamomun aromaticum (Chinese cinnamon) are the leading varieties consumed. Ceylon cinnamon is also referred to as "true cinnamon", while the Chinese variety is known as "cassia". While both are relatively similar in characteristics and both feature a fragrant, sweet and warm taste, the flavor of the Ceylon variety is more refined and subtle. Ceylon cinnamon is more rare in North America than the cassia, the less expensive variety, which is the most popular in the United States.

Possibly most the common baking spice, Cinnamon is used in cakes, cookies, and desserts throughout the world. Cinnamon is also used in savory chicken and lamb dishes from the Middle East. In American cooking, Cinnamon is often paired with apples and used in other fruit and cereal dishes. Stick Cinnamon is used in pickling and for flavoring hot beverages.

Cinnamon has a sweet, woody fragrance in both ground and stick forms.

Cinnamon's unique healing abilities come from three basic types of components in the essential oils found in its bark. These oils contain active components called cinnamaldehyde, cinnamyl acetate, and cinnamyl alcohol, plus a wide range of other volatile substances.