This book is a fiftieth anniversary republication of Thomas Nagel's "What Is It Like to Be a Bat?", a classic article in the philosophy of mind. Through its argument for the irreducible subjectivity of consciousness, it played an essential role in making the study of consciousness a central part of philosophy, psychology, and neuroscience. It also spurred the now flourishing scientific attention to the consciousness of non-human creatures: mammals, birds, fish, mollusks, and insects. The book also includes a second essay offering Nagel's more recent thoughts on the most promising positive response to the mind-body problem, as posed in the original essay.