Caffeine is a natural substance that is present in over 60 plant species. Alternative names include theine, guaranine and mateine. It is consumed by humans in the form of beverages such as coffee, tea, chocolate and soft drinks. Coffee was first discovered in Arabia during the 9th century, and was originally cultivated in Ethiopia. Tea was first drunk in China and cacao was discovered in South America. During the 15th century, coffee became popular all over the world. The most common species of coffee are Coffea arabica (Arabica coffee) and Coffea canephora (Robusta coffee), which respectively account for 80-90% and 10-20% of world-wide production. Coffee is the product which contains the highest and most variable quantity of caffeine in the human diet. This book discusses more about the consumption of caffeine, the side effects it may have on the human body, and its impact of an individual's performance and mood once consumed.