During a scientific career of more that 60 years, Clarence Clay made many important research contributions spanning a wide range of topics in ocean acoustics, acoustical oceanography, geophysical exploration, signal processing, SONAR system applications and techniques, and more. His achievements are detailed in over 135 peer-reviewed articles, abstracts, technical reports, and at least five patents. In addition he was the author, or co-author, of four widely read textbooks. His research work is recognized internationally for the far-reaching significance of many of the advances he made. In order to attempt a proper appreciation of the range and versatility of Clay's accomplishments, within the constraints of a 30 minute presentation, this talk will consist of a series of brief overviews of a representative selection of topics on which he worked. These include: the theory and measurement of rough surface scattering, particularly at the ocean boundaries; matched-filter signal transmission and detection, time reversal, and matched-field processing; acoustic methods and models for scattering from individual fish, and for fish detection and abundance estimation; the theory and experimental investigation of time domain scattering from wedges, and its incorporation into wedge assemblage models; and the theory and applications of seismic exploration and profiling. © 2012 Acoustical Society of America.