Common mullein (Verbascum thapsus L.) is a medicinal plant readily found in roadsides, meadows and pasture lands and has been used to treat pulmonary problems, inflammatory diseases, asthma, spasmodic coughs, diarrhoea and migraine headaches. Although it has been used medicinally since ancient times, the popularity of common mullein has been increasing commercially for the past few years. Today, the dried leaves and flowers, swallow capsules, alcohol extracts and the flower oil of this plant can easily be found in health stores in the United States. The use of common mullein extracts in folk medicine begun recently to be supported by an increasing number of research studies. This paper thoroughly reviews all the scientific research related to Verbascum thapsus L. including plant tissue cultures and the biological properties of this plant.