Ambient Noise (AN) research during World War II was facilitated by the availability of calibrated instruments and motivated by the necessity to understand AN levels in coastal waters. The state-of-the-art was reviewed by Knudsen in 1948 and later by Pryce and Urick in 1954. After the war, AN research waned until the classic paper by Wenz (1962) marked its renaissance. By 1976, a vast literature existed on measurements, theory and computational methods, and in the 1980s AN was the second largest area of underwater acoustics. Initially, emphasis was on the omni-directional properties of the field and later on vertical/horizontal directionality and the shipping-component statistical characteristics. Measurement arrays characterized the statistics of the AN, its persistent directionality, and benchmarked attempts to predict the AN-levels. Interest in AN sources re-emerged around 1985 with the identification oceanic bubble ensembles as a major contributor to deep and shallow water noise fields. This overview discusses fundamental AN sources, measurements, and the physics of the air–sea interaction boundary layer. Bubble, spray, splash, and rain noise are examined and ranked in order of importance. The production, absorption, and transmission of sound by bubble clouds and layers produced by breaking waves are examined. [Work sponsored by ONR.]