An aircraft content distribution system comprising: a server installed in an aircraft that includes a plurality of passenger seats; a plurality of clients, each client being configured to output content to a respective display device associated with at least one of the passenger seats; and a processing resource for distributing a plurality of items of content to the plurality of clients, wherein each client is configured to transmit at least one message to the server representative of portions of the items of content that are present or not present at that client, the system further being characterised in that the processing resource is configured to determine from the messages portions of the items of content that are missing from at least one client, and to distribute the missing portions of content to the clients via a wireless local area network according to a multicast protocol that is at least one of a connectionless or unreliable, each client is configured to monitor whether it has received substantially all portions of the content and perform a synchronisation process with the server and, independently of whether one or more other of the clients have received all portions of the content and independently of whether the processing resource is continuing to distribute missing portions of the content, each client is configured to enter a local control mode in response to having received substantially all portions of the content and on completion of the synchronization process, each client comprises a processor and a storage device for locally storing the plurality of items of content, for each of the clients, in the local control mode, a user can enter a series of interlinked menus on the respective display device and a said user can select one of the locally stored items of content and the processor of the client is configured to stream the selected item of content to the respective display device for display in response to the selection, regardless of whether the processing resource is continuing to distribute missing portions of the content to other of the clients, and wherein the processing resource is further configured to distribute all of the missing portions of content to all of the plurality of clients. a server installed in an aircraft that includes a plurality of passenger seats; a plurality of clients, each client being configured to output content to a respective display device associated with at least one of the passenger seats; and a processing resource for distributing a plurality of items of content to the plurality of clients, wherein each client is configured to transmit at least one message to the server representative of portions of the items of content that are present or not present at that client, the system further being characterised in that the processing resource is configured to determine from the messages portions of the items of content that are missing from at least one client, and to distribute the missing portions of content to the clients via a wireless local area network according to a multicast protocol that is at least one of a connectionless or unreliable, each client is configured to monitor whether it has received substantially all portions of the content and perform a synchronisation process with the server and, independently of whether one or more other of the clients have received all portions of the content and independently of whether the processing resource is continuing to distribute missing portions of the content, each client is configured to enter a local control mode in response to having received substantially all portions of the content and on completion of the synchronization process, each client comprises a processor and a storage device for locally storing the plurality of items of content, for each of the clients, in the local control mode, a user can enter a series of interlinked menus on the respective display device and a said user can select one of the locally stored items of content and the processor of the client is configured to stream the selected item of content to the respective display device for display in response to the selection, regardless of whether the processing resource is continuing to distribute missing portions of the content to other of the clients, and wherein the processing resource is further configured to distribute all of the missing portions of content to all of the plurality of clients.