This book offers a complete and well-organized review of the latest advances made in developing ultra-weak chemiluminescence techniques for analytical applications. It systematically introduces the current theories, mechanisms, instruments, technologies, and real applications of ultra-weak chemiluminescence. Compared to books devoted to the normal chemiluminescence and bioluminescence, this book covers a wide range of ultra-weak chemiluminescence based on inorganic chemical reactions and nanotechnology from a principle and practical point of view. This book is intended for readers who are interested in expanding their knowledge of chemiluminescence and employing ultra-weak chemiluminescence techniques to develop new detection methods for analytical applications.