Abstract <p>This paper presents the results of a study of hydrodynamic instability in the collapse of shells, in particular shaped-charge liners. Initially, this instability was initiated by harmonic surface perturbations or perturbations of the load parameters. The instability was manifested in the development of these perturbations over time. The absence or limited growth of surface perturbations was considered as a manifestation of the stability of the shell deformation process. In this paper, both numerical simulation results and available experimental data are considered. Based on the results of the study, conclusions are drawn about the causes and possible forms of manifestation of instability in the deformation of collapsing metal shells, the governing parameters of this process, and its features and mechanism.</p>