A method of delivering content over a network for use at a device, the method comprising: receiving, by a content server, a request for content from the device, wherein the content comprises playable content; sending, by the content server, to a delivery prediction function a request for a content readiness estimate for the requested content; determining, by the delivery prediction function, the readiness estimate by estimating when the content will be ready for use at the device according to a predetermined criterion, based on network conditions affecting delivery of the content from the content server to the device, wherein the predetermined criterion is that the content can be used continuously or without interruption, without having to pause in order to receive further content before use can recommence, wherein the readiness estimate relates to the time estimated as being required to buffer content at the device prior to commencement of playback to provide continuous or uninterrupted playback, and wherein the determining step further comprises, upon determining that movement of the device between network cells is possible or likely before use of the content is commenced at the device, performing the estimating step while taking into account data relating to historical mobility of the device amongst a plurality of network cells visited by the device, with network conditions within those visited cells influencing the performance of the estimating step; receiving, by the content server, the readiness estimate from the delivery prediction function; sending, by the content server, a response to the device providing the readiness estimate; and sending, by the content server, the requested content to the device at a time selected by a user of the device to download the requested content. receiving, by a content server, a request for content from the device, wherein the content comprises playable content; sending, by the content server, to a delivery prediction function a request for a content readiness estimate for the requested content; determining, by the delivery prediction function, the readiness estimate by estimating when the content will be ready for use at the device according to a predetermined criterion, based on network conditions affecting delivery of the content from the content server to the device, wherein the predetermined criterion is that the content can be used continuously or without interruption, without having to pause in order to receive further content before use can recommence, wherein the readiness estimate relates to the time estimated as being required to buffer content at the device prior to commencement of playback to provide continuous or uninterrupted playback, and wherein the determining step further comprises, upon determining that movement of the device between network cells is possible or likely before use of the content is commenced at the device, performing the estimating step while taking into account data relating to historical mobility of the device amongst a plurality of network cells visited by the device, with network conditions within those visited cells influencing the performance of the estimating step; receiving, by the content server, the readiness estimate from the delivery prediction function; sending, by the content server, a response to the device providing the readiness estimate; and sending, by the content server, the requested content to the device at a time selected by a user of the device to download the requested content.