This article aims to summarize the current state of knowledge on St. John's wort (Hypericum perforatum L.) which is one of the oldest and best investigated medicinal herbs. Dried alcoholic extracts are the most important preparations on the market although a variety of other preparations are available. Depressive disorders according to modern diagnostic standards are the best known and most widely investigated indication although the more traditional, broader indication of 'psycho-vegetative disorders, depressive disorders, anxiety and/or nervous agitation', including diagnoses such as somatoform disorders, might more adequately describe what Hypericum extracts are actually used for by many practitioners. The exact mechanisms of action are still unclear, but the available research clearly shows that various bioactive constituents contribute to the clinical effects reported, often in a synergistic manner. Hypericum extracts have consistently shown activity in pharmacological models related to antidepressant effects. Randomized clinical trials show that Hypericum extracts are more effective than placebo and similarly effective as standard antidepressants while having better tolerability in the acute treatment of major depressive episodes. The most important risk associated with Hypericum extracts are interactions with other drugs. Therefore, physicians need to be informed whether their patients take St. John's wort products. If the risk of interactions is adequately taken into account, high quality Hypericum extracts are an effective and safe tool in the hand of qualified health profession-als in primary care.