Theobromine (theobromide), also known as xantheose, is a bitter alkaloid of the cacao plant, with the chemical formula C₇H₇N₄O₂. It is found in chocolate, as well as in a number of other foods, including the leaves of the tea plant, and the kola (or cola) nut. It is in the methylxanthine class of chemical compounds, which also includes the similar compounds theophylline and caffeine. (In caffeine, the only difference is that the NH group of theobromine is an N-CH₃ group.) Despite its name, the compound contains no bromine—theobromine is derived from Theobroma, the name of the genus of the cacao tree, (which itself is made up of the Greek roots theo ("God") and brosi ("food"), meaning "food of the gods") with the suffix -ine given to alkaloids and other basic nitrogen-containing compounds.

Theobromine is a slightly water-soluble (330 mg/L), crystalline, bitter powder; the colour has been listed as either white or colourless. It has a similar, but lesser, effect than caffeine in the human nervous system, making it a lesser homologue. Theobromine is an isomer of theophylline, as well as paraxanthine. Theobromine is categorized as a dimethyl xanthine.