I invited world-recognized scientists who are specialists in design and synthesis of phthalocyanine materials field to contribute specific chapters to this monograph. This was in order to cover major aspects of non-linear optics from the fundamentals to various applications. The monograph in general presents a balanced and informative description of progress in molecular non- linear optics, includes the preparation of stable phthalocyanine material systems like actual nonlinear materials, building of a knowledge base and an intuitive understanding of structure/function relationships in simple molecular systems. Dr.rer.nat.Tamer E. Youssef