This book highlights the rapidly emerging field of solution-processed halide perovskite lasers. These amazing materials not only possess exceptional photovoltaic properties, but are also outstanding optical gain media. Halide perovskites are the latest member of solution-processed optical gain media, joining organics and traditional semiconductor colloidal quantum dots. Amplified spontaneous emission and lasing have been demonstrated in various halide perovskite configurations and nanostructures with wavelengths tunable over the visible and infrared wavelengths (400β1000 nm). This book provides comprehensive information on perovskite lasing, starting with some fundamentals of lasers and their basic operating principles. Unambiguous methods for identifying lasing light emission are presented, while the basic optoelectronic properties of perovskite materials are also discussed, with an emphasis on their photophysics, using ultrafast optical spectroscopy techniques. The viability of perovskites as a gain media within a suitable resonator, as well as the characterization methods for optical gain, are highlighted. The book closes with a discussion on the remaining challenges (such as electrical driven lasing and material stabilities) that need to be tackled, and the future of this new family of lasers.