Rhododendron, the largest genus of the family Ericaceae, includes 1200 species, distributed throughout Northeast Asia and Eurasia, Western Europe and North America. Rhododendron arboreum possess various pharmacological activities like oxytocic, oestrogenic, CNS depressant, hepatoprotective, anti-diabitic, anti-inflammatory and anti-microbial. Traditionally leaves of R. arboreum use in the treatment of gout and rheumatoid arthritis (RA) and flowers in the treatment of cancer. Rheumatoid arthritis is a chronic, systemic autoimmune disorder that causes the immune system to attack the joints, where it causes inflammation (arthritis) and destruction. On the basis of traditional uses, it was decided to explore the immunomodulatory, anti-tumor and anti-microbial principles from the leaves and flowers of Rhododendron arboreum. This book will provide the kind of information that will be of interest to those who work or plan to begin work in the captivating areas of phytochemistry, immunomodulation, plant tumor activity and microbiology.