Book excerpt: This book assembles both theory and application in this field, to interest experimentalists and theoreticians alike. Part 1 is concerned with the theory and computing of non-linear optical (NLO) properties while Part 2 reviews the latest developments in experimentation. This book will be invaluable to researchers and students in academia and industry, particularlrly to anyone involved in materials science, theoretical and computational chemistry, chemical physics, and molecular physics.