This textbook is intended for all graduate students and researchers interested in the young and rapidly evolving field of microclusters. In many ways microclusters (consisting typically of 10-103 atoms) can be considered as a new phase of matter, intermediate between a solid and a molecule or, alternatively, between the macroscopic and microscopic world. The interest in microclusters is motivated both by their fundamentally new physical properties and by their potential applications in areas such as electronics, catalysis, chemical engineering, and photography. The book is designed for newcomers to the field and offers the reader a lucid description of the fundamental physics of all types of microclusters.