It is a typical but often dreaded music reference question—‘‘Can you help me figure out what this song is?’’—accompanied by the humming of a sometimes unrecognizable tune segment. Print resources like thematic catalogs and notation indexes can help identify a small group of classical music works, but successful use of these sources requires a combination of mathematics, transcription, and luck. However, technology has made it easier to answer this kind of question when one is faced with the plethora of popular music melodies, even when the patron cannot recall the lyrics to a particular song. Harnessing, organizing, and providing access to an unwieldy amount of recorded music has seemed nearly impossible. For years, research in music information retrieval (MIR) systems has been underway using experimental tools and creative programs that address such complicated issues as multiple recordings of the same work, differences in recording quality, tempo variances, and algorithm creation. MIR is the umbrella over a variety of more specific topics from metadata to programming, with a fascinating history and innovative projects on the horizon (see Resource List for further reading). The MIR systems discussed in this column—Midomi and Shazam—are only two of many, but I selected them because they are free and mobile. Both systems have applications for the iPhone, BlackBerry, and other cell phone brands so that music discovery, identification, and sharing can take place anywhere. These two systems can thus be used on the go, and they can also assist librarians trying to answer that [in]famous reference question.