The purpose of "Encyclopaedia of Atomic Spectra and Atomic Structure" is to provide teachers with recent researches that allows students to share. The powerful demonstrations will build a strong foundation for all students-The present approach is designed to meet this need by stressing the physical or observable aspects of theory - an extensive use of electronic charge density. Thus, it determines directly the sizes and shapes of molecules, their electrical moments and, indeed, all of their chemical and physical properties. Since the charge density describes the distribution of negative charge in real space, it is a physically measurable quantity. The book is undertaken chiefly from the experimental point of view, with structure and properties of the nucleus as discussed in the light of the experimental results. The book is self-contained, complete and updated. The book has been written in a systematic manner that should enable the students to appreciate how each new idea emerge from the earlier works. The chapters are well arranged and the solved numerical problems based on those chapter. The book has been written in an easy readable and lucid manner.