Since their theoretical prediction in 1997, Interatomic (intermolecular) Coulombic Decay (ICD) and related processes have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the discovered electronic decay phenomena and by the exciting possibility of their practical application, for example in spectroscopy of interfaces. Interatomic decay phenomena take place in inner-shellionized and inner-shell-excited clusters due to electronic correlation between two or more cluster constituents. These processes lead to relaxation by electron emission and often also to disintegration of the resulting positively charged cluster. Here we review the recent progress in the study of interatomic decay phenomena in excited, singly and multiply charged clusters.