Calamus may mean:

• Sweet flag (Acorus calamus), an herb
• Calamus (palm genus), a genus of rattan palms
• Calamus (fish genus), a genus of porgies (Sparidae)
• Calamus, Iowa
• Calamus, Wisconsin
• Calamus, a Desktop Publishing application
• Calamus, a character in the poem Dionysiaca by 4th century Greek writer Nonnus
• Calamus (poem), a series of poems by American writer Walt Whitman.