Recently there has been an interest in the utilization of plant biotechnology for production of valuable secondary metabolites, e.g. pharmaceuticals, fragrances, pigments, flavours. Centaurium erythraea is an endangered medicinal plant species, which aerial parts named Centaurii herba represent official drug included in the European Pharmacopoeia. In the present book we desribe in vitro cultures of C. erythraea as potential source of medicinally important secoiridoid glucosides (sweroside, swertiamarine and gentiopicroside). Shoot cultures growing on solid and in liquid media, somaclonal variation event, genetic transformation and obtaining of transformed plants are described in the book with details. The secoiridoid glucosides production was also determined in the all obtained cultures. Special attention is given to the bioreactor system for propagation of shoots and production of secoiridoid glucosides. The analysis should help shed some light on in vitro cultures of this medicinal plant as a source of secoiridoid glucosides, which may be especially useful to biologists, pharmacists, biotechnological industry or anyone else who is interesting in plant in vitro cultures.