Walnuts (Juglans regia L.) belong to the family Juglandaceae and are a good source of fat, protein, vitamins and minerals along with phenolics which act as antioxidants. Walnuts are ranked second after blackberries for their antioxidant activities. Walnuts have high levels of melatonin (sleep hormone and antioxidant) and vitamin E. They are also a rich source of L-arginine, phospholipids, proteins, tocopherols, polysterols, squalene and unsaturated fatty acids. The whole walnut tree including the seeds, leaves, husks, nuts and kernels are rich in active phytochemicals and natural antioxidants, which have been proven to ameliorate/prevent many diseases including cardiovascular disease, diabetes, obesity, cancer, neurological diseases, etc. Walnuts are unique among nuts in that they are highest in alpha-linolenic acid (ALA - omega-3 fatty acid) levels. Hence, it they are gaining more importance in medicinal and pharmaceutical industries. In the last few decades, there has been tremendous interest in the use of walnuts as evidenced by the voluminous scientific work along with consumer's health awareness. This chapter will describe the medicinal properties and importance of walnuts.