The article analyzes the X-ray crystallographic structure of exoribonuclease RNase II from Escherichia coli. The structure of RNase II from Escherichia coli and point mutant, D209N, that allows RNA binding are also studied. Exoribonucleases belong to three groups of proteins, the RNB, DEED and PDX families. The structure of these three groups are also analyzed and explained.