This is the first part to be published of a two-part volume on the East Riding liberty and wapentake of Howdenshire. It deals with the nineteen civil parishes and townships which made up the liberty outside the town of Howden itself. Until 1836 Howdenshire was one of the bishop of Durham’s exempt franchises in Yorkshire, enclaves which survived the Reformation and Civil War. Its special nature, which is mostly ancient wetland reclaimed in the twelfth century, is explored via in-depth sections on drainage and river defence, with a reconstruction of the unique medieval and early modern scheme developed to contain the River Ouse and empty the drainage dykes.