This book reviews the growing literature that is consistent with the hypothesis that hormones can regulate auditory physiology and perception across a broad range of animal taxa, including humans. Understanding how hormones modulate auditory function has far reaching implications for advancing our knowledge in the basic biomedical sciences and in understanding the evolution of acoustic communication systems. A fundamental goal of neuroscience is to understand how hormones modulate neural circuits and behavior. For example, steroids such as estrogens and androgens are well-known regulators of vocal motor behaviors used during social acoustic communication. Recent studies have shown that these same hormones can also greatly influence the reception of social acoustic signals, leading to the more efficient exchange of acoustic information.