Hypericum L. is a genus of the family Hypericaceae within the dicotyledones. The constituents of Hypericum species are valued for their important biological properties. Their use is in the treatment of depression and as antibacterial agents has been well documented in the primary literature and in ethnobotanical reports. The present contribution gives a comprehensive summary of the chemical constituents of members of the genus Hypericum and their biological effects. A detailed account of the chemical constituents, including phloroglucinol derivatives, xanthones, dianthrones, and flavonoids, is included. These compounds show a diverse range of biological activities that include antimicrobial, cytotoxic, antidepressant-like, and antinociceptive effects.