The Hitchin district, covering much of north Hertfordshire and a small part of south-east Bedfordshire, straddles the north-eastern extremity of the Chiltern Hills. The central part of the area is dominated by the ever-growing conurbations of Stevenage, Letchworth and Hitchin. Luton covers the south-western corner. Beyond these towns, the area is one of contrasting scenery which reflects the underlying geology. This work describes the results of the geological survey of the district. It highlights the stratigraphy of the chalk, which can now be related to sequences on the south coast, and also the complex interrelationship of the glaciogenic deposits proved within the Hitchin Gap.