This book covers the principles, operation, and applications of the modern micro-nano devices being developed to address global twenty-first-century challenges. The subject of this book is Micro-Nano Systems in the twenty-first century. The major areas of applications cover medical diagnostics, 5G/6G communication, inertial, space, geography and resource exploration, defense, aviation, etc. This book provides the readers with a comprehensive outlook on the topics to help understand the physical scientific principles and techniques being applied to the design and development of devices, sensors, and actuators using Micro-Nano System Technology (MST). The book addresses fabrication technologies such as CMOS-MEMS, Piezoelectric, and other special MEMS processes, where novel transducers are being designed and developed for ultrasound, energy harvesting, data storage, computing, inertial, fluidics, optomechanical, etc. The book serves as a tutorial guide to graduate students, researchers, engineers, other large technical audiences, and also the general public to understand these topics in a systematic and more thorough way by providing a range of illustrations, comparative charts/tables, equations, analysis, and plots/graphs. In a nutshell, the book is designed to provide a didactic approach to explaining scientific facts and figures in more lucid ways. The students will get the engineering and scientific know-how of modern micro and nano system technology, a range of transduction principles, and potential applied application areas. Readers will understand (through first-hand equations, principles of operations, solved examples, notes, several illustrations, and graphs) how to design, and develop a range of applications in microsystem technology.