A method comprising: a controller receiving, on a touch-screen graphical display within a control interface of a first controller application, input data indicating selection of one or more particular audio tracks for playback by one or more particular playback devices (502, 504); and the controller transmitting, via a network interface to a playback device, an instruction to create a playback queue (512, 514, 516) associated with the one or more particular playback devices that includes the one or more particular audio tracks, wherein the playback device is one of the one or more particular playback devices; characterized by further comprising: the controller receiving, via the network interface in response to the instruction to create the playback queue (512, 514, 516), a first queue update message data indicating a first version number of the playback queue (512, 514, 516), wherein the first version number is updated whenever the playback queue is altered by one or more controllers or one or more control applications configured to control playback by the playback device; the controller storing, in a queue version state variable, an indication of the first version number of the playback queue (512, 514, 516); receiving a second queue update message from the playback device, the second queue update message indicating a second version number of the playback queue (512, 514, 516); based on the second version number of the playback queue (512, 514, 516) not matching the first version number of the playback queue (512, 514, 516) stored in the queue version state variable of the controller, determining, by the controller, that a version of the queue stored by the controller is out of date; and in response to determining that the version of the queue stored by the controller is inconsistent with a version of the queue associated with the one or more particular playback devices, the controller transmitting, via a network interface to the computing device, an instruction to replace all tracks in the playback queue (512, 514, 516) with the one or more particular audio tracks. a controller receiving, on a touch-screen graphical display within a control interface of a first controller application, input data indicating selection of one or more particular audio tracks for playback by one or more particular playback devices (502, 504); and the controller transmitting, via a network interface to a playback device, an instruction to create a playback queue (512, 514, 516) associated with the one or more particular playback devices that includes the one or more particular audio tracks, wherein the playback device is one of the one or more particular playback devices; characterized by further comprising: the controller receiving, via the network interface in response to the instruction to create the playback queue (512, 514, 516), a first queue update message data indicating a first version number of the playback queue (512, 514, 516), wherein the first version number is updated whenever the playback queue is altered by one or more controllers or one or more control applications configured to control playback by the playback device; the controller storing, in a queue version state variable, an indication of the first version number of the playback queue (512, 514, 516); receiving a second queue update message from the playback device, the second queue update message indicating a second version number of the playback queue (512, 514, 516); based on the second version number of the playback queue (512, 514, 516) not matching the first version number of the playback queue (512, 514, 516) stored in the queue version state variable of the controller, determining, by the controller, that a version of the queue stored by the controller is out of date; and in response to determining that the version of the queue stored by the controller is inconsistent with a version of the queue associated with the one or more particular playback devices, the controller transmitting, via a network interface to the computing device, an instruction to replace all tracks in the playback queue (512, 514, 516) with the one or more particular audio tracks. the controller receiving, via the network interface in response to the instruction to create the playback queue (512, 514, 516), a first queue update message data indicating a first version number of the playback queue (512, 514, 516), wherein the first version number is updated whenever the playback queue is altered by one or more controllers or one or more control applications configured to control playback by the playback device; the controller storing, in a queue version state variable, an indication of the first version number of the playback queue (512, 514, 516); receiving a second queue update message from the playback device, the second queue update message indicating a second version number of the playback queue (512, 514, 516); based on the second version number of the playback queue (512, 514, 516) not matching the first version number of the playback queue (512, 514, 516) stored in the queue version state variable of the controller, determining, by the controller, that a version of the queue stored by the controller is out of date; and in response to determining that the version of the queue stored by the controller is inconsistent with a version of the queue associated with the one or more particular playback devices, the controller transmitting, via a network interface to the computing device, an instruction to replace all tracks in the playback queue (512, 514, 516) with the one or more particular audio tracks.