The Chiltern Hundreds was an ancient administrative area in Buckinghamshire, England, composed of three "hundreds" and lying partially within the Chiltern Hills. "Taking the Chiltern Hundreds" now refers to the legal procedure used to effect resignation from the British House of Commons. This is because the ancient office of Crown Steward and Bailiff for the area, having been reduced to a mere sinecure by the 17th century, became the first to be used in this resignation procedure a century later. Other titles were also later used for the same purpose, but at present only the Chiltern Hundreds office and the Crown Steward and Bailiff of the Manor of Northstead are used.
The three Chiltern Hundreds
A hundred was a traditional division of an English county that could raise one hundred fighting men for the Crown. The three Chiltern Hundreds were Stoke Humdred, Desborough Humdred, and Burnham Humdred. Despite their collective name only Desborough Hundred was located within the area defined by the Chiltern Hills in Buckinghamshire. The area had been Crown property as early as the 13th century.
Steward and Bailiff
Through the Saxon and early Norman periods the area was administered by an elder. But by the late Middle Ages the office holder was elected from among a hundred's notable landholding families. As the area was wild and notorious for outlaws, a Steward and Bailiff was appointed directly by the Crown (thus as a Royal baliwick it was a legal office answerable to the reigning monarch) to maintain law and order. However by the end of the 16th century the position no longer served its original purpose because the hundreds were now administered by local officials or new royal posts established in every county, who ensured that Royal commands and laws were obeyed. In the 17th century the office of Steward and Bailiff was reduced to just a title with no attached powers or duties.
As it was still nominally a Crown office, the post of Crown Steward and Bailiff of the three Chiltern Hundreds of Stoke, Desborough and Burnham became the first title to be used in the procedure developed in the 18th century for resignation from the British House of Commons by Members of Parliament (MPs). While no longer having any actual role or responsibility, it is a nominal office for profit under the Crown: holding such an office disqualifies an MP from the House under the constitutional Act, the Act of Settlement 1701. The first use of this office to allow an MP to resign was in 1751 - for John Pitt. Other offices were later used but now only this office and Crown Steward and Bailiff of the Manor of Northstead are used.