Holy Basil (Ocimum sanctum) is a widely grown, sacred plant of India. It belong to the labiateae family. It is also called by names like Manjari/Krishna tulsi (Sanskrit), Trittavu (Malayalam), Tulshi (Marathi) and Thulsi (Tamil and Telegu). It is called Holy Basil in English. The natural habitat of Tulsi varies from sea level to an altitude of 2000 m. It is found growing naturally in moist soil nearly all over the globe. In India, Hindus grow Tulsi as a religious plant in their homes, temples and their farms. They use Tulsi leaves in routine worship. This plant is also grown as a pot herd and in home gardens. In addition to Ocimum sanctum proper, some other species on varieties of this plant also go by the same name viz Tulsi. These are Ocimum canum (Ram tulsi or Kali tulsi), Ocimum basilicum or bobai tulsi, Ocimum kilmand, O. scharicum or camphor tulsi, etc. The medicinal effect of all these varieties is nearly similar, if not the same. The best part of the matter is that certain Indian scientists are at the threshold of finalizing their discovery of a reliable medicine against cancer out of Tulsi plant. Tulsi is one of the most important plants of Haryana and India. Therefore more research is needed for large scale cultivation of the plant in vacant lands and spaces. More research is also required in the use of Tulsi leaves, oil and extracts for a large number of medicinal uses and as an organic insecticide. The Ch Devi Lal Herbal Nature Garden is involved in researching and cultivating many medicinal herbs including Tulsi and Safed Musli. The need for an authentic but comprehensive and broad based book on Tulsi has been long felt. Therefore, all available data is well documented in a scientific manner for the use as reference to students, research scholars, scientists engaged in the field of medicinal plants. This publication is an effort in that direction.