Question: What is the name of the association that the Chelsea Building Society is a member of?
Context: The Portman Building Society was a mutual building society in the United Kingdom, providing mortgages and savings accounts to consumers and offering loans to commercial enterprises.  Its head office was in Bournemouth and its administration centre in Wolverhampton.  Portman merged with the Nationwide Building Society in August 2007, at which time it was the third largest building society in the UK and the largest regional building society in the south of England, with 154 branches and assets exceeding £15 billion. The Chesham Building Society was a building society based in the market town of Chesham in Buckinghamshire, England which merged with the Skipton Building Society in June 2010.  Prior to the merger it was the 37th largest building society in the United Kingdom based on its total assets of £231 million.  It was a member of the Building Societies Association. The Cheshire Building Society was a building society based in Macclesfield, Cheshire, England.  It was the 11th largest building society in the United Kingdom based on total assets of £5 billion on 31 December 2007, prior to merging with the Nationwide Building Society, and was a member of the Building Societies Association.  The Cheshire was acquired by Nationwide on 15 December 2008, which was as a result of its approach to the Nationwide in September 2008 regarding a possible merger due to its financial position. The Cambridge Building Society is a UK mutual building society based in Cambridge, Cambridgeshire, England.  It is the 14th largest in the United Kingdom based on total assets of £1,128 million at 31 December 2015.  It is a member of the Building Societies Association.  The Society was formed in 1850 as the Cambridgeshire Permanent Benefit Building Society, adopting its current name in 1945.  There is no connection between this Society and the Cambridge Foresters’ Benefit Building Society which was dissolved in 1960 or the Cambridge Peers Economic Building Society which was dissolved in 1972. The Scottish Building Society is a building society based in Edinburgh, Scotland.  It is the oldest building society in the world, the only building society based in Scotland and the 42nd largest in the United Kingdom based on total assets of £377.6 million at 31 January 2015.  It is a member of the Building Societies Association. The Dunfermline Building Society was a building society and later a trading division of Nationwide Building Society, based in Dunfermline, Fife, Scotland.  Before its 2009 merger with Nationwide, it was the largest building society in Scotland and the 12th largest in the United Kingdom based on total assets of £3.3 billion at 31 December 2007.  It was a member of the Building Societies Association. Chelsea Building Society is a trading name of Yorkshire Building Society based in Bradford, West Yorkshire.  Chelsea merged with the Yorkshire in 2010, at which point Chelsea was the fourth largest building society in the United Kingdom, with assets in excess of £13 billion.  Chelsea has 35 branded branches, mainly in the southern areas of England with a large number of these in London. Derbyshire Building Society (previously trading as The Derbyshire) was a UK building society based in Duffield, Derbyshire in the East Midlands of England.  It was the 9th largest building society in the United Kingdom based on total assets of £7.1 billion at 31 December 2007, until it was acquired by Nationwide Building Society (Nationwide) on 1 December 2008.  It operated as a trading division of the society, with 50 branches, until it was fully integrated into its parent in November 2014. The Principality Building Society, (Welsh: "Cymdeithas Adeiladu'r Principality" ), is a Welsh building society based in Cardiff, the capital of Wales.  With assets of £8bn it is the largest building society in Wales and the sixth largest in the United Kingdom.  Principality Building Society is mutual, which means it is owned by its members rather than shareholders.  It serves clients through the internet and telephone as well as at high street branches.  It is a member of the Building Societies Association. The Yorkshire Building Society is the third largest building society in the UK, with its headquarters in Bradford, West Yorkshire, England.  It is a member of the Building Societies Association.
Answer: Building Societies Association