Design and performance characteristics are examined of four representative Small Innovative Reactors (SIRs)—IRIS, PBMR, 4S and ENHS. It is shown that SIRs have a number of useful attributes, including the following: Reduced number of components and design simplicity; High degree of modularity, with complete modules fabrication and assembly in factory; Elimination of severe accidents by design leading to enhanced safety; Simplified operation and maintenance; Enhanced proliferation resistance; Close match between demand and supply of electricity; Short construction time; Long plant life; Investment protection; Cost effective approach to technology development. It is concluded that SIRs have significant differences in their design features and performance characteristics from large size reactors that justify taking a thorough examination of the desirability of their commercialization.