A micromechanical analysis of deformation and fracture in creeping alloys is presented based on a mechanistic approach using continuum mechanics. The analysis was first carried out on a coarse microscopic level in which the self-consistent theory of Hill was employed to treat the steady state creep of heterogeneous alloys with coarse microstructures allowing for grain boundary sliding. Processes operating on a finer scale than the grain size such as grain boundary diffusion and surface diffusion were subsequently included in the analysis. It was found that the high stresses required for cavity nucleation occur at intergranular particles only in transients of grain boundary sliding, and that two modes of cavity growth result corresponding to rate control by each of the abovementioned diffusional processes.Creep cavitation in 304 stainless steel in the neighborhood of 0.5 Tm was studied experimentally to test these theoretical models. Our results suggest that a broad spectrum of interfacial energy may exist and that microstructural changes such as those caused by twins can alter cavitation behavior drastically. Cavities grow in most cases by grain boundary diffusion coupled with matrix creep, somewhat restricted by surface diffusion. However, the grain boundary sliding can be a dominant mode of cavity growth at high stresses and for large cavities.