The book consists of ten chapters that present the results of the research work on ionic effect on nucleic acid. The structure and stability of several non-natural triplets are also analysed and comparison has been made with that of natural triplets of nucleic acid. Each chapter explains the objective of the work, and focuses on results and conclusion based on the findings. The thorough explanations of the ab initio method used in the study are included. Both quantum mechanics and molecular mechanics calculations used in the work are illustrated in this chapter.