This book is a revised and translated edition of the Japanese book "Chobiryushi" (Ultra-Fine Particles). It describes many original efforts made in Japan to explore the world of Ultra-Fine Particles (UFPs) and was written with the following in mind: (1) to share with scientists and engineers the intriguing scientific aspects of ultra-fine particles and to show their potential as new materials; and (2) to entice researchers to participate in the development of this emerging field.

Applications for UFP technologies tend towards refinement and control and are deeply related to the fields of electronics and bioengineering. The Ultra-Fine Particle Project also included a group that investigated biological and chemical applications in anticipation of such needs. Nonbiological UFPs with sizes on the same order as cells or microscopic bodies within cells are expected to interact with microscopic biological bodies in ways that are as yet unknown. The book is in a sense a comprehensive introduction to the UFP (nanoparticles) world.