At present, the demand for Rosmarinus officinalis is increasing due to its use in traditional medicine, pharmaceutical industries, cosmetic fields and agribusiness, food preservation and fragrance industries, aromatherapy and for the quality of their essential oil. Significant variations in the chemical composition of the essential oils of Rosemary as well as its aroma and its medicinal characteristics (antimicrobial and antioxidant properties) have been reported with relation to the geographic origin. Moreover, the antimicrobial activities of Hexane Crude Extracts (HCE) and hydrodistilled essential oils of Rosmarinus officinalis leaves are tested in vitro by paper disc bioassay methods and showed high antibacterial inhibition activities and moderate antifungal inhibition. Phytochemical screening results showed that the antimicrobial activity of the HCE of the leaves of Rosmarinus officinalis is due to the presence of flavonoids, phenolic compounds and triterpene. This book, therefore, create awareness about the health benefits and nutritional values of this plant and also the use of naturally bioactive molecules to control pathogens that cause diseases in plants and humans.