A process for the preparation of reduced graphene comprising the steps of: providing an expandable graphite intercalated with oxygen containing groups; heating the expandable graphite under conditions sufficient to cause expansion of the expandable graphite and formation of an expanded graphite comprising oxygen containing groups; and contacting the expanded graphite with carbon monoxide to reduce at least a portion of the oxygen containing groups and form a reduced expanded graphite comprising an array of reduced graphene. The process of the invention enables large volumes of high quality graphene to be produced.