Soft errors are becoming an important issue for deep submicron technologies. To protect circuits against soft errors, designers routinely introduce modular redundancy to detect and correct these errors. A commonly used technique, Double Modular Redundancy (DMR) involves duplication of the basic module. Conventionally, DMR only allows error detection since voting cannot be used to determine the module in error. Recently, however, it has been found that DMR can, for some circuits, be enhanced to provide soft error correction as well as detection. The general approach, DDMR (Diverse DMR), relies on introducing design diversity between the original and redundant modules so that they produce different error patterns when a soft error occurs. The module in error can be found by examining these patterns. Herein, the generalized approach is described. A number of techniques for producing diverse designs with distinct error patterns are identified and illustrated with examples. New DDMR solutions are presented and finally, the future direction of DDMR research is discussed.