Photochromic polymer systems are of two main types - those which are merely solid solutions of photochromes in polymeric matrices and those custom-designed polymers which inherently exhibit photochromism. This book provides a concise review of developments in such systems over the past two decades. The coverage has been limited specifically to applied systems, or areas with potential applications, although over 500 references cite much of the literature on the fundamentals of the subject. The book aims to complement existing and recent books on photochromism which deal with low molecular weight photochromic systems mainly from a more fundamental perspective. It should appeal to industrial and academic researchers in materials science, chemistry, physics and electronics.