Bletchley Park, in Milton Keynes, Buckinghamshire, England, was the central site of the United Kingdom's Government Code and Cypher School (GC&CS), which during the Second World War regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers.

The official historian of World War II British Intelligence has written that the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and that without it the outcome of the war would have been uncertain. The site is now an educational and historical attraction memorialising and celebrating those accomplishments.

Fifty miles (80 km) northwest of London, the site appears in the Domesday Book as part of the Manor of Eaton. Browne Willis built a mansion there in 1711, but after Thomas Harrison purchased the property in 1793 this was pulled down. It was first known as Bletchley Park after its purchase by Samuel Lipscomb Seckham in 1877. The estate of 581 acres (235 ha) was bought in 1883 by Sir Herbert Samuel Leon, who expanded the then-existing farmhouse into the present "maudlin and monstrous pile" combining Victorian Gothic, Tudor, and Dutch Baroque styles.

In 1938, the mansion and much of the site was bought by a builder planning a housing estate, but in May 1938 Admiral Sir Hugh Sinclair, head of the Secret Intelligence Service (SIS or MI6) bought the mansion and 58 acres for use by GC&CS and SIS in the event of war.

Block B houses the main collection relating to the wartime codebreaking efforts, including the rebuilt bombe and the Enigma machine collection, extensive displays relating to wartime codebreaking and espionage generally, and Stephen Kettle's life-size statue of Alan Turing,

As well as The National Museum of Computing, the park is also home to a number of other exhibits.

The Mansion
Bletchley Park Garage
Home Front Display exhibits include rationing, evacuation, the Blitz, war-time wash day, and "Make Do & Mend".
The American Garden Trail – celebrates the continuing links between the UK and the US which were so important to victory
65th Nachrichten Abteilung – a German World War II Signals Group, depicting a receiving and transmitting station with many items of original equipment, including an Enigma machine.
Pigeons at War – tells of the important role played by Britain's 250,000 homing pigeons during the war.
Children's Corner
On 18 June 2014, the museum was officially re-opened by Catherine, Duchess of Cambridge when it was revealed that her paternal grandmother, Valerie, and Valerie's twin sister, Mary (née Glassborow) had both worked at Bletchley Park during the war. The twin sisters both worked as Foreign Office Civilians in Hut 6, where they managed the interception of enemy and neutral diplomatic signals for decryption. Valerie married Catherine's grandfather Peter Middleton, who was a civilian staff member at Bletchley.