The book is an up-to-date introduction to the fundamentals of the initial stages of Electrocrystallization, which are dominated by nucleation and growth of the first clusters of the new phase. It offers a readable exposition of the topic, in simple terms, providing a detailed theoretical description of the phenomena involved. The most relevant aspects of the experimental studies of electrochemical nucleation and growth are considered, as well, including some important methods for acquiring and analyzing experimental results. Having specific properties quite different from those of bulk materials, these small, nano-clusters have always attracted considerable attention, and many sophisticated methods have been developed for cluster studies. In spite of this, information on small clusters can still be obtained by simple experiments, and the book shows that Electrocrystallization is unique in this respect. In this special case the phase change may be controlled experimentally by controlling the voltage and current, two simple and easily measurable electrical quantities. Certainly, this is what makes electrochemical systems an attractive object of study both from a scientific and from a practical point of view. The book is suitable not only for specialists in Electrocrystallization but also for graduate and PhD students, as well as for scientists from diverse but related fields like pure and applied electrochemistry, electrocatalysis, corrosion, electrochemical adsorption and materials science.