This book highlights the process of heat applications driven by modular high-temperature gas-cooled reactors (HTGRs) which have inherent safety characteristics and high outlet temperature. The book systematically covers related principles, guidelines and discussion about circuits, components and the coupling with HTGR, recommendations of safety measures, and economic and environmental requirements, with examples and experience from long-term practice. The combination of the HTGR technology and process heat applications not only is important for promoting the use of HTGR but also provides an option of significant potential for the replacement of conventional fossil fuels. With over a thousand illustrations, the book is of outstanding reference value for researchers and professionals to develop a thorough understanding.