Abstract Fault-tolerant controllers (FTCs) have recently gained considerable attention due to their important role in maintaining the safety of modern technological systems via configured redundancy. The basis of a FTC through an analysis of the requirements of safety-critical systems is introduced in this paper. The development of passive FTC approaches, including their advantages and disadvantages, is discussed based on safety requirements. Closely associated with the safety-relevant issues, recent progress in active FTC design methodologies is reviewed in the sequence of fault detection and diagnosis (FDD), reconfigurable controls, and integration of FDD and reconfiguration. In summary, it is the view of this paper that addressing safety issues is the key to further development of FTCs.