The m5C-MTases form a closely-knit family of enzymes in which common amino acid sequence motifs almost certainly translate into common structural and functional elements. These common elements are located predominantly in a single structural domain that performs the chemistry of the reaction. Sequence-specific DNA recognition is accomplished by a separate domain that contains recognition elements not seen in other structures. This, combined with the novel and unexpected mechanistic feature of trapping a base out of the DNA helix, makes the m5C-MTases an intriguing class of enzymes for further study. The reaction pathway has suddenly become more complicated because of the base-flipping and much remains to be learned about the DNA recognition elements in the family members for which structural information is not yet available.