Metal ions play essential role in biological systems. They are very effective in controlling an enzyme catalyzed reaction and without them biochemical reactions catalyzed by certain metalloenzymes would precede either very slowly or not at all. Many studies are being carried out on the interaction of metal ions with nucleic acids both in the experimental and theoretical levels. Such studies, when carried out in theoretical levels, help experimental researchers to rationalize their problems and eliminate guess works to large extents. The book emphasizes the use of Density functional theory (DFT) method in exploring the interactions of metal ions specially Zn (II) and Cu(I) ions with various nucleic acid bases. The frontier orbital approach (HOMO-LUMO) of the study indicates an alternate way for the predictions of the most favorable interactions between the metal ion and nucleobases. Importance of the HOMO-LUMO energy gap in predicting the most favorable attachments of metal ions with bases is thoroughly studied.