'This is not a play. This is a poem in several registers, set at night on the Severn Estuary. Its subject is moonrise, which happens five times in five different forms: new moon, half moon, full moon, no moon and moon reborn. Various characters, some living, some dead, all based on real people from the Severn catchment, talk towards the moment of moonrise and are changed by it. The poem, which was written for the 2009 festival of the Severn, aims to record what happens when the moon moves over us - its effect on water and its effect on voices' - Alice Oswald. A Sleepwalk on the Severn is a poem for several voices, set at night on the Severn Estuary. Its subject is moonrise, which happens five times in five different forms: new moon, half moon, full moon, no moon and moon reborn. Various characters, some living, some dead - all based on real people from the Severn catchment - talk towards the moment of moonrise and are changed by it. Commissioned for the 2009 festival of the Severn, Alice Oswald's breathtakingly original new work aims to record what happens when the moon moves over the sublunary world: its effect on water and its effect on language.