Formation of small solid and liquid particles is vital for a variety of natural and technological phenomena, from the evolution of the universe, through atmospheric air pollution and global climate change. Despite its importance, nucleation is still not well understood, and this unique book addresses that need. It develops the theory of nucleation from first principles in a comprehensive and clear way, and uniquely brings together classical theory with contemporary atomistic approaches. Important real-world situations are considered, and insight is given into cases typically not considered such as particle formation in flames and plasmas. Written by an author with more than 35 years of experience in the field, this will be an invaluable reference for senior undergraduates and graduate students in a number of disciplines, as well as for researchers in fields ranging from climate science and astrophysics to design of systems for semiconductor processing and materials synthesis.