This paper presents a discussion of functional silence in contemporary classical music with a particular focus on the music of Salvatore Sciarrino and Jürg Frey, two composers whose drastically-contrasting bodies of work both occupy the interstitial space between the audible and inaudible. To begin, I address three main questions: what are the functions of silence in a musical context, how do the characteristics of a work affect our perception of these silences, and how do these functions relate to our perception of music on the edge of silence. In answering these first two questions, I discuss three categories of silence---temporal, spatial, and gestural---which I use in a silence-centric analyses of Sciarrino's Let me die before I wake, Allegoria della notte, and Infinito Nero, as well as Frey's Streichquarttet III. To further apply these concepts to music on the edge of silence, I provide a fourth category---timbral silence---which describes the perception of absence or silence within the presence of sound and allows for the application of existing functional principles of silence to sounding events. In turn, this allows us to understand the music of Sciarrino and Frey in terms of timbral completion and timbral dissolution, respectively. Having established a theoretical framework for understanding the function of silence, the second half of this paper discusses the composition of A Moment on the In-between, my 2018 work for string quartet, with a focus on the intentional application of these principles of functional silence within the piece.