The "cocktail-party effect" - the ability to focus on one voice in a sea of noises - is a highly sophisticated skill that is usually effortless to listeners but largely impossible for machines. Investigating and unravelling this capacity spans numerous fields including psychology, physiology, engineering, and computer science. All these perspectives are brought together in this volume which, for the first time, provides a comprehensive and authoritative discussion of our understanding of how humans separate speech, and the state of the art in approaching these abilities with machines. This material is drawn from an October 2003 workshop, sponsored by the National Science Foundation, on speech separation. Leading authorities from around the world were invited to present their perspectives and discuss the points of contact to other perspectives. The result is a clear and uniform overview of this problem, and a primer in what is emerging as an important, active and successful area for the development of new techniques and applications. Chapters include historical and current summaries of relevant research in behavioral science, neuroscience and engineering, along with more in-depth descriptions of several of the most exciting current research projects and techniques, including the latest experimental results illuminating how listeners organize the mixtures of sound they hear, and the most powerful and successful signal processing and machine learning techniques for the separation of real-world recordings of sound mixtures by one or more microphones. There is no comparable collection that seeks to bring together the underlying experimental science and the wide variety of technical approaches to give an integrated picture of the problem and solutions to speech separation. Those specializing in speech science, hearing science, neuroscience, or computer science and engineers working on applications such as automatic speech recognition, cochlear implants, hands-free telephones, sound recording, multimedia indexing and retrieval will find Speech Separation by Humans and Machines a useful and inspiring read.