The book focuses on the role of ubiquitin proteasome system (UPS) in central nervous system. Proteasomes are large multicatalytic proteinase complexes that are found in the cytosol and in the nucleus of eukaryotic cells with a central role in cellular protein turnover. The UPS has a central role in the selective degradation of intracellular proteins. In addition to serving as a means to rapidly eliminate short-lived regulatory proteins involved in cell cycle, cell growth, and differentiation, in periods of stress rapid elimination of denatured, misfolded and damaged proteins by the proteasome becomes a critical determinant of cell fate. These aspects are analysed in central nervous system physiology and pathology.