Hypericum extract preparations are used extensively in many countries to treat mildly to moderately depressed patients. While this was based previously on traditional experience, extensive research over the last 10 years has given a broad preclinical and clinical basis to justify the use of Hypericum as an antidepressant. This book reviews the available data related to the biochemical, functional, and behavioural pharmacology of Hypericum and its active constituents. The clinical chapters overview the evidenced basis for its use as an antidepressant, initial data in anxiety and somatoform disorders, and the site effect profile of Hypericum and its possible relevant drug interactions. The known pharmacokinetics of the relevant constituents and the biopharmaceutical quality of commercially available Hypericum preparations are also discussed.