Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is used as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to the adenosine A1 receptor, which enhances release of the neurotransmitter acetylcholine. Caffeine has a three-dimensional structure similar to that of adenosine, which allows it to bind and block its receptors. Caffeine also increases cyclic AMP levels through nonselective inhibition of phosphodiesterase. In the present book, twenty-three typical literatures about caffeine published on international authoritative journals were selected to introduce the worldwide newest progress, which contains reviews or original researches on caffeine. We hope this book can demonstrate advances in caffeine as well as give references to the researchers, students and other related people.