The RNase II family of enzymes is ubiquitous and has crucial roles in the processing, degradation and quality control of all types of RNA. These exoribonucleases processively degrade RNA from the 3'-end releasing 5'-nucleotide monophosphates. In prokaryotes, RNase II and RNase R have two N-terminal CSD and one C-terminal S1 domain involved in RNA binding, and a central catalytic RNB domain. In eukaryotes, Rrp44p/Dis3, is a RNase II-like protein with similar modular organization, that is the only catalytically active nuclease in the exosome, a complex crucial for RNA metabolism. Here we review recent progresses in the understanding of the degradation mechanism of RNase II, based on mutational analysis and their characterization regarding catalysis and RNA affinity. We have given particular emphasis on E. coli RNase II but the synergies between the functional and structural studies have shown that our findings have implications in the understanding the similar mode of action of other RNase II family members.