Take a look around the bus or subway and see just how many people are bumping along to an iPod or an MP3 player. What they are listening to is their secret, but the many signature earbuds in sight should give one a real sense of just how pervasive digital audio has become. This article describes how that popularity is mirrored in library audio services, where audio circulation continues to gain momentum nationwide. Downloadable music files are making room for audiobooks available through downloading services, and the audio industry hopes that familiarity with the MP3 format will bring more customers into the ranks of audiobook listeners. Nonprint library services now largely involve digital media: users borrow audiobooks on CD, but they also download audiobooks, music, and videos and check out Playaways that have audio programs in a self-contained, battery-powered player. The newly announced industry moves toward MP3, aimed at generating retail sales, will send library audio circulation through the roof in the next few years. Libraries are doing an excellent job of making audio more visible to patrons--moving their entire collections to the front of the library, integrating listening into audiobook clubs, trying new formats, and generally encouraging patrons to give audio a try.