Cavitation instabilities have been predicted for a single void in a ductile metal stressed under high triaxiality conditions. In experiments for a ceramic reinforced by metal particles a single dominant void has been observed on the fracture surface of some of the metal particles bridging a crack, and also tests for a thin ductile metal layer bonding two ceramic blocks have indicated rapid void growth. Analyses for these material configurations are discussed here. When the void radius is very small, a nonlocal plasticity model is needed to account for observed size-effects, and recent analyses for the influence of such size-effects on cavitation instabilities are presented. When a metal contains a distribution of micro voids, and the void spacing compared to void size is not extremely large, the surrounding voids may affect the occurrence of a cavitation instability at one of the voids. This has been analyzed for a material containing a periodic distribution of spherical voids with two different void sizes, where the stress fields around larger voids may accelerate the growth of smaller voids. Another approach has been an analysis of a unit cell model in which a central cavity is discretely represented, while the surrounding voids are represented by a porous ductile material model in terms of a field quantity that specifies the variation of the void volume fraction in the surrounding metal.