Lanthanides plays important role in the modern era of chemistry as one of the emerging field because of ts application both in clinical and biochemical research. Because of its various co-ordination numbers in easily accessible spectral regions, absorption spectra opens a new age in the modern chemistry. The book comprises of five chapters. First chapter explains the general features of Lanthanides including its scope in medicinal, biological and clinical fields. Second chapter focus on the various spectral properties of Lanthanides both magnetic as well as optical properties. The third chapter elaborate the structure of nucleosides and nucleotides along with their general properties. Fourth chapter focus on the details analysis of the interaction of Pr (III) with the selected nucleoside and nucleotide in the presence and absence of Ca (II) which plays a vital role in human metabolism. Numbers of tables and figures are enclosed to show the details of the spectral analysis of the interaction of Pr (III)and nucleic acid components. This solution studies can predict the possible structure of the complexes of Pr(III) theoretically. The book helps academically for the researchers.