Abstract : Recent deep-submicron technology-based ICs are significantly more vulnerable to transient faults. The arisen errors are thus also more critical than they have ever been before. This thesis presents a further novel benefit of the Quasi-Delay Insensitive (QDI) asynchronous circuits in terms of reliability: their strong natural ability to mitigate longduration transient faults that are severe in modern synchronous circuits. A methodology to evaluate comparatively the transient-fault effects on synchronous and QDI asynchronous circuits is presented. Furthermore, a method to obtain the transient-fault mitigation ability of the QDI circuits' memory elements (i.e., the C-elements) is also proposed. Finally, mitigation techniques are suggested to increase even more the Celements' transient-fault attenuation, and thus also the QDI asynchronous systems' robustness.