Bacterial diseases are a great challenge in the health system and the treatment of these diseases continues to be a big problem in the modern day. Natural product medicine have been used since the ancient times to treat microbial diseases and proved to be efficient drugs to cure ailments. Achillea millefolium L. has proven to be an efficient anti-bacterial drug due to the presence of many secondary metabolites including flavonoids, sesquiterpenoids and phenolic acids. The phenolic acids and flavonoids are mainly responsible for the antibacterial activity of A. millefolium. Achillea millefolium L. shows great anti-bacterial potential against many common bacteria like S. aureus, E. coli, K. pneumoniae, P. aeruginosa, S. epidermidis, B. cereus etc. In this book, a comprehensive review of antibacterial activity of Achillea millefolium L. is presented against different types of gram positive and gram negative bacteria which will be a good contribution in literature and promising for future research in pharmacological fields.