Small systems are a very active area of research and development due to improved instrumentation that allows for spatial resolution in the range of sizes from one to 100 nm. In this size range, many physical and chemical properties change, which opens up new approaches to the study of substances and their practical application. This affects both traditional fields of knowledge and many other new fields including physics, chemistry, biology, etc. This book highlights new developments in statistical thermodynamics that answer the most important questions about the specifics of small systems - when one cannot apply equations or traditional thermodynamic models.