In this book, renowned scientists describe the complexity of exoplanetary atmospheres and all of the observational techniques that are employed to probe them. Readers will also find a panoramic description of the atmospheres of the planets within the Solar System, with explanation of considerations especially relevant to exoplanets. Over the past few years, thousands of exoplanets have been discovered orbiting around stars relatively close to the Solar System. Astronomers have revealed how varied these exoplanets are (rocky, icy, giant) and how diverse their architecture can be, confirming science fiction images in several cases and extending beyond the human imagination in others. The natural next step is to study their atmospheres and to understand their chemical composition and the physical processes taking place in their interiors, with the aim of detecting biomarkers. This book will appeal to all who seek a comprehensive, state-of-the-art account of the latest knowledge in the rapidly developing and highly interdisciplinary field of exoplanet research.