Nucleoside analogs play a major role especially in the anticancer and antiviral therapy. A number of modern anticancer and antiviral drugs contain these substances. Derivatives of these ring systems are interesting as antimetabolic agents in biochemical reactions. Recently, considerable efforts have been made to prepare other novel heterocyclic nucleosides to improve the antitumor efficacy, few examples are reported for the synthesis of heterocyclic nucleosides using microwave activation. In recent reports from our laboratory, we described the preparation of different novel functionalized heterocyclic nucleosides, we had already reported the use of some novel heterocyclic nucleosides as substrates or inhibitors in the protein glycosylation process. These common features encouraged us to develop a simple, eco-friendly and cost-effective methodologies for synthesis of heterocyclic nucleosides using microwave activation. The aim of this book was to address the use of microwave activation and their advantages in the synthesis of medically important heterocyclic nucleosides.