This paper forms the Introduction to the ICPhS-07 Special Session “Sound to Sense” (S2S). S2S is a Marie Curie Research Training Network (funded May 2007-2011) for interdisciplinary research on modeling the role of fine phonetic detail in speech understanding/recognition by humans and machines. The special session includes four position papers that illustrate some of the subject areas and aims of S2S, and two discussion papers. This Introduction sets the scene by defining what fine phonetic detail is, describing the theoretical motivations for investigating its influence on speech processing, and outlining why it is timely to investigate its role in how speech is understood.