Proton decay: spectroscopic probe beyond the proton drip line

Proton decay has been transformed in recent years from an exotic phenomenon into a powerful spectroscopic tool. The frontiers of experimental and theoretical proton-decay studies will be reviewed. Different aspects of proton decay will be illustrated with recent results on the deformed proton emitter $^{135}$Tb, the odd–odd deformed proton emitter $^{130}$Eu, the complex fine structure in the odd–odd $^{146}$Tm nucleus and on excited states in the transitional proton emitter $^{145}$Tm