After water, tea signifies the second most frequently consumed beverage world-wide. Teas are not all the same; among the many areas of research that are included in this book are the effects of selenium-containing green tea on food consumption and body weight gain. Research shows that tea consumption may have its strongest effect among patients with cardiovascular disease. A specific chapter investigates whether green tea intake can reduce the risk of chronic obstructive pulmonary disease. Research is presented to show that green tea and its major constituent epigallocatechin gallate (EGCG) have a potential chemopreventative and/or treatment for a variety of diseases including breast cancer. Other research sheds new light on the molecular basis for the cancer-preventive activity of EGCG in vivo and helps in the design of new strategies to prevent cancer. A further study presents an analysis assessing the progress of research on the mechanisms pertaining to how telomerase activity is regulated by green tea in cancer cells. Further chapters look at the relationship of tea to diabetes and a description of the beneficial effects of green tea catechins on neuronal functions and neuronal diseases such as dementia. To improve biological functions and industrial applicability of green tea and its by-products, research is presented showing irradiation as a useful method.