MP3 players are often described as music collections in our pockets or the pocket jukebox. Indeed, it would seem that MP3 players have significantly transformed music collections, music collecting practices, and contemporary understandings of the music collection. The MP3 player may be used to store, retrieve, and reproduce digital music files, and, therefore, it can be described as a portal—if we define the term portal as an entrance, doorway, or gateway—into these simulated (Baudrillard, 1983) mobile music collections. It is an interface between the human body and archives of digitally compressed music. This can perhaps be understood as constituting a kind of musical cyborg, a cybernetic organism, a hybrid of human and machine (Haraway, 1991). The MP3 player, in this hybridised sense, is a gateway into the digital, virtual, or simulated (Baudrillard, 1983) material cultural realm of music, a mobilised cyber-collection. The question then is what becomes of the music collection and the music collector when music shifts from the objectified disc and spool to the digital compression format and MP3 player portal? And, what are the social and cultural implications of the MP3 player portal’s increasing pervasiveness and embeddedness in the flows of everyday life? The purpose of this article is to briefly introduce and discuss these questions alongside some of the technical details of the MP3 player. This article aims to use the material and technical details and definitions of the MP3 player to open up a range of possible questions that may be pursued in future research in this area. I will begin by defining the MP3 and the MP3 player.