The book is intended for an audience already familiar with proton and carbon NMR and commencing research in phosphane chemistry (broadly defined). It is the primary aim of this book to enable the reader to identify the main factors governing the phosphorus chemical shift values in the 31P-NMR spectrum and to make an educated guess as to where the phosphorus resonance(s) of a given target compound can be expected. It is not within the scope of this book to enable one to predict a phosphorus chemical shift precisely or even within a reasonable margin of error, with a few notable exceptions. The further intent of this book is to assist the reader in determining important issues like bond order, p-bonding contributions from substituents, the existence or non-existence of metallacycles etc., in short, to make structural assignments without the aid of X-ray crystal structure determinations and to explain structural differences in solution and the solid state where appropriate.