This chapter discusses the music theory and aural skills practiced daily by an important and influential segment of the public: the session musicians, engineers, songwriters, and producers in the recording studios and publishing houses of Nashville’s Music Row. Through interviews with leading engineers and studio musicians, the chapter reveals that particular kinds of music theoretical knowledge and aural skills are valued in these contexts. Efficiency and accuracy are prized during recording sessions, and there are high expectations for the fluid and immediate application of practical knowledge and skills to writing, recording, producing, and performing music. While some in these situations have had formal, academic training in music theory, that is not true of everyone. Some terminology from academic music theory is valuable, but there is also the need for additional terminology and systems in order to develop a common language for all participants. This chapter provides detailed information about an important aspect of this common language, the Nashville Number System, a musical shorthand developed within the studios of Music Row that now has currency among musicians around the world, bringing music theory to an ever-expanding public.