The famous Hereford world map, the 'Mappa Mundi', dates from around 1300, and was painted on one skin of calf-parchment, less than 1 mm thick and measuring about 130 cm square. When we read of its frequent ordeals, we may marvel that it is still in good condition and can be examined. Yet, it is by no means the oldest surviving mappamundi, nor was it the largest: the Ebstorf map (destroyed by bombing in 1943) was of similar age and almost three times bigger. Mappaemundi may be square or round, large or small, extremely simple or amazingly complex. Their geography is unfamiliar and many of their fauna are grotesque. Their importance is enormous: for their encyclopaedic ambition, for their place in devotional and romanesque iconography and for their attempts to document contemporary world views. In setting the Hereford world map in context, P.D.A. Harvey and his twenty-four collaborators introduce us to medieval ideas of the world and man's place in it in ways that will excite historians, geographers, students of art history, theologians, and anyone interested in the medieval world view.