The ocean science community has invested heavily in coordinating systems developed to make ocean observations. The Global Ocean Observing System (GOOS) is a research program developed to coordinate ocean observing systems. Expert panels identify requirements for the systems in terms of Essential Ocean Variables (EOVs). The absence of sound in the list of EOVs should be striking to most ocean acousticians. Sound propagates so well in the ocean that it is the best way to probe the marine environment over long distances. Marine organisms have evolved ways to use the physics of underwater sound for biosonar, to communicate, and to orient. During the industrial age, humans have developed similar tools, and sources such as commercial shipping have elevated ocean noise. A working group of the Partnership for Observation of the Global Oceans and linked to the International Quiet Ocean Experiment has developed a description of an Essential Ocean Variable for the Acoustic Environment designed to facilitate monitoring of the sound field of the oceans globally over decades, to model how human and natural sources create the sound field, and to define effects of changes in sound fields on marine life at the individual, population, and ecosystem levels.