Methods for efficient download of a data package and a client device and server that may implement such methods are disclosed. The client device sends an inventory identifying existing stored content packages to the download server. The download server identifies portions of the requested data package already corresponding to content elements already stored on the client device, and sends information to the client device indicating which portions of the requested data package are already stored on the client device. The client device gathers the already-stored portions of the requested data package and requests a remaining portion of the requested data package from the download server. The download server receives the request for the remaining portion of the requested data package and sends the remaining portion to the client device.