This chapter focuses on various detailed effects of caffeine on mood. It aims to challenge the way in which most caffeine research has been conducted by looking at the issue from a different angle. The chapter discusses the pros and cons of the various approaches that some “aware” scientists have implemented in their research. Actual experimental evidence of the effects of caffeine has been documented in hundreds, possibly thousands, of publications covering probably more than 100 years of research. Tea and coffee seem to be more similar in their subjective effects when using similar caffeine contents or when corrected for differences in caffeine dose. Of all of the research performed on the effects of caffeine on mood and performance to date, possibly the most interesting is that which focuses on differences in sensitivity to the effects of caffeine.