Basic science research has led to new understanding of the mechanisms of pathology underlying dysfunction in the ear, nose, and throat. This research is defining new interventions that modulate biochemical events leading to pathology and may one day offer new opportunities to prevent and treat impairment. Clearly, many of the advances in our basic understanding and promises for new interventions to prevent and treat pathology are based upon molecular and biochemical studies defining the primary and secondary signaling molecules controlling cellular development and homeostasis, including response to age and stress factors. A key influence increasingly appreciated as contributing to pathology, consequent to many etiological factors, and affecting essentially all tissues and organ systems is the delicate balance that must be maintained in the level of cellular free radicals. While free radicals are essential in the maintenance of normal cellular function, their excess induces cell injury and death. Free radicals directly facilitate biochemical reactions necessary for cell life and participate in cell signaling or “redox signaling,” e.g., nitric oxide control of vascular tone. As will be demonstrated in this book, free radical biology is emerging as a defining force determining normal function and, in excess, a common pathway to cell death associated with many etiologies leading to ENT pathology. This book will examine the current state of free radial biology as it impacts on hearing, otology, laryngology, rhinology, and head and neck function. Our intent is to highlight the interrelationship of basic and translational studies in each area, to define the challenges to translation, and to identify the existing basic issues that demand investigation as well as the opportunities for novel intervention to prevent and treat ENT pathology and impairment. In each chapter, or in some cases pairs of chapters, the authors have been charged to include and where possible marry issues of basic research with translational challenges and research, defining the pathway by which new basic insights may lead to interventions to prevent or treat impairment.