This book features a collection of overview articles by both Russian and international authors on a range of pressing topics in chemical physics. Its publication coincides with the centenary of the birth of the great 20th-century scientist and Nobel laureate Nikolai Nikolaevich Semenov. The volume reflects the evolution of Semenov's ideas and concepts in the fields of chain reactions, the theory of chain and thermal explosions, and includes his own review. As one of the key founders of chemical physics, Semenov always viewed the discipline as a science that applies a physical approach to the study of various chemical phenomena, anticipating the growing role of biology in contemporary and future chemistry. Many of the articles in this book embody this "Semenovian" understanding of chemical physics and address its new and relevant challenges. This work is sure to captivate anyone interested in the major trends shaping the development of chemical science at the turn of the 20th and 21st centuries, as well as the anticipated key directions for chemistry in the coming century.