Quasicrystals are a new form of the solid state which differ from the other two known forms, crystalline and amorphous, by possesing a new type of long-range translational order, called quasiperiodicty, and a noncrystallographic orientational order. This book provides an up-to-date description of the unusual physical properties of these new materials. Emphasis is placed on the experimental results, which are compared with those of the corresponding crystalline and amorphous systems and discussed in terms of modern theoretical models. Written by leading authorities in the field, the book will be of great use both to experienced workers in the field and to uninitiated graduate students.