1. A method comprising: causing a control device to display a control interface comprising an area associated with at least an artist name, an album name, and a track name associated with a first audio track that is being played by one or more playback devices that are carried in respective housings that are different from a housing carrying the control device, wherein the one or more playback devices are controlled via the control device over one or more first networks comprising a local area network; receiving, via the control device, input data representing a selection of a location in the area of the control interface, the location corresponding to search criteria indicating one or more of: the artist name, the album name, and the track name; responsive to receiving the selection of the location, identifying, via the control device, at least two audio sources that are accessible for searching from the control device, wherein the at least two audio sources comprise (i) one or more streaming audio services that provide respective libraries of streamable audio tracks and (ii) a media library comprising additional audio tracks that are represented by respective files which are stored in one or more local data storages on the control device, wherein the files stored in the one or more local data storages are each different from files representing the streamable audio tracks; searching, via the control device, the at least two audio sources across multiple search classification fields supported by the at least two audio sources for second audio tracks corresponding to the search criteria, the multiple search classification fields comprising artist name, album name, and track title, wherein the second audio tracks are different from the first audio track, and wherein searching the at least two audio sources comprises: (i) sending, via a network interface of the control device over one or more second networks comprising a wide area network, respective search queries to the one or more streaming audio services for the second audio tracks corresponding to the search criteria; and (ii) searching the media library for the second audio tracks corresponding to the search criteria; retrieving, via the control device, data representing search results from the at least two audio sources based on the search, wherein the search results indicate the second audio tracks corresponding to the search criteria; and causing the control device to display a tabbed control interface, each tab corresponding to a respective search classification field and including a respective list of second audio tracks matching the respective search classification field, wherein the respective second audio tracks of each list are grouped into two or more groups within the respective list according to their respective audio source of the at least two audio sources; receiving, via the control device, input data representing a selection of one or more particular second audio tracks from among the second audio tracks indicated by the search results; and causing, via the network interface of the control device, the one or more playback devices to play back the selected one or more particular second audio tracks, wherein playing back the selected one or more particular second audio tracks comprises at least one playback device of the one or more playback devices streaming the one or more particular second audio tracks from at least one of the at least two audio sources and the one or more playback devices playing the streamed one or more particular second audio tracks via one or more speakers.