In recent years, there has been considerable interest in the role of antioxidants. The most important function of these compounds in living organisms is protection against free radicals, which are responsible for the many diseases, including cardiovascular diseases, diseases of the nervous system, and cancers. The human body produces some of the antioxidants (e.g., glutathione), while food is the source of others. Particularly remarkable is purine alkaloid—caffeine. Thanks to its biological activity and the possibilities of transformation of molecule, caffeine is an excellent starting compound in the synthesis of new derivatives with potential pharmacological properties, which in the future may find application in the treatment of Parkinson's disease, Alzheimer's disease, or various types of cancers. This chapter focuses on the biological activity of caffeine and its analogs, which, in addition to antioxidant properties, can act as adenosine receptors antagonist, the MAO inhibitor, and a protective agent against free radicals. © 2020 Elsevier Inc. All rights reserved.