A unique textbook about the fundamentals of Process Intensification: The theoretical and conceptual basis of the discipline are discussed. How to use that conceptual basis in the practical development of intensified chemical and biochemical processes is explored. Interdisciplinarity presents a key feature of Process Intensification - therefore, the material contained in the book reaches far beyond the classical area of chemical engineering. Developments in other disciplines, such as chemistry, catalysis, energy technology, applied physics, electronics and materials science, which are relevant to Process Intensification are extensively described and discussed in the book from the chemical engineers perspective. The book consists of three major parts: In the first part, the PI principles are introduced, discussed in detail and illustrated with practical examples. The second part is entirely devoted to fundamental approaches of Process Intensification in four domains: spatial, thermodynamic, functional and temporal, described as Structure, Energy, Synergy and Time, respectively. The third and final part of the book is explores to the methodology for applying the fundamental PI-approaches in practice. The close relation to sustainable (including inherently safe) processing is addressed. Several case studies of diverse types of chemical processes are presented.