This work deals with polypyrazolylborates (scorpionates), a class of ligands known since 1966, which have become increasingly popular with inorganic, organometallic and co-ordination chemists since 1986, because of their versatility and user-friendliness. They can be readily modified sterically and electronically though appropriate substitution on the pyrazole ring and on boron, and have led to a number of firsts in co-ordination chemistry (first stable CuCO complex, first monomeric MgR complex). Over 170 different scorpoinate ligands are known today. This book is intended as a reference work, placing at the researcher's command almost all of the 1500 or more references on the subject up to 1999, organized both according to the ligand type and according to the metal or metalloid being co-ordinated. It acquaints the reader with the special features of this ligand system and permits an assessment of what has been done in a given sub-area, and of which areas remain relatively unexplored. It presents procedures for ligand synthesis, and also covers their use in catalysis and in the modelling of biologically active substances.