This book has been almost entirely rewritten, but its purpose and general organization remain the same as those of previous editions. The Introduction to the first (1945) edition included the following paragraph: The reasons for writing this book were, firstly, the conviction that the structural side of inorganic chemistry cannot be put on a sound basis until the knowledge gained from the study of the solid state has been incorporated into chemistry as an integral part of that subject, and secondly, the equally stroing conviction that it is unsatisfactory merely to add information about the structures of solids to the descriptions of the elements and compounds as usually presented in a systematic treatment of inorganic chemistry.* Now, after a period of thirty years during which considerable advances have been made in solid state chemistry, it is still true to say that the structures and properties of solids receive very little attention in most treatments of inorganic chemistry, and this in spite of the fact that most elements and most inorganic compounds are solids at ordinary temperatures. This state of affairs would seem to be sufficient justification for the appearance of yet another edition of this book.