Numerous factors influence the chemical quality of medicinal plants from crop establishment to extraction of raw material. The most important ones are described using the example of Hypericum perforatum. Optimization of these factors contributes to the objective of producing a high-quality drug, and a method consisting of three scientific approaches (technological, agronomical, plant breeding) is presented. All data concerning the plant (biology, physiology and environmental impacts) and the active components and by-products (pathway, localization and stability) are useful to adapt and to develop management sequences. Although plant breeding appears to be the principal way of improvement, and gives good results in terms of resistance to pathogens, active component content and yield; the agronomical and the technological approaches are also very important. The technological approach after harvesting is especially important to avoid degradation of the active components and to induce, in some cases, the transformation of by-products to those molecules sought. This integrated method (plant breeding and agronomical and chemical approaches) requires research on different levels of organization from molecule to field, and includes all processing systems from farmers to chemists.