NMR spectroscopy is one of the most useful tools to get reliable information about both the geometrical and the electronic structures of small-size (containing few atoms) to large-size (containing thousands of atoms) molecules. It can also give information about subtle and intrinsic characteristics of those molecules or chemical processes in which the nuclei that resonate by NMR are involved. To get this information requires both the computation and theoretical analysis of the spectroscopic parameters. This book provides a basic presentation, which is as thorough as possible, of the most commonly used theories and models for the theoretical understanding and calculation of the spectroscopic parameters of NMR spectroscopy. This information is combined with their applications in both, model systems and complex systems, the analysis of few newest effects together with highly accurate calculations for small-size molecules and their calculations in large-sized compounds, ionic liquids, heavy-atom containing systems, lanthanide and actinide systems and solid-state quantum systems. The authors have been encouraged to present the most insightful ideas and the most important findings that one can get from NMR spectroscopy as well as its limitations or drawbacks. This book is aimed at undergraduate and graduate students, specialists and, possibly, industry workers who will find information about the theoretical developments that have been performed in the last decade enabling them to achieve highly accurate calculations and understandings that were not available previously. The book also offers clarity in the exposition of abstract concepts that are not usually communicated, together with simple and complex applications.