The Scottish Parliament elections take place on 3 May, but 12 MSPs will not be taking on the fight to regain their seats.
Eleven out of the 12 were elected to the first Holyrood in 1999. They include ex ministers Susan Deacon and Jim Wallace, the Presiding Officer George Reid and Independent MSP Dennis Canavan.
SUSAN DEACON: LABOUR (1999-2007)
The Edinburgh East and Musselburgh MSP was handed the health portfolio in the first Holyrood administration run by First Minister Donald Dewar.
But she left the ministerial ranks after declining an offer from Jack McConnell to take up the social justice post in his first cabinet.
Ms Deacon made life difficult for the Scottish Executive from the backbenches by questioning policies on education, crime and the relocation of civil service jobs. She also rallied Labour MSP opposition to the Iraq War in 2003.
The politician said it was time to move on after eight years, but also expressed disappointment that Holyrood had become "tightly controlled" by the political parties.
JANIS HUGHES: LABOUR (1999-2007)
The former nurse enjoyed a lower profile than other MSPs during her time in parliament, generally backing the executive and supporting the Jack McConnell Labour leadership contest.
The Rutherglen MSP showed a rebellious streak by abstaining from voting on plans for a massive shake-up of Glasgow's hospital provision.
She said it was "time to move on and do other things".
KATE MACLEAN: LABOUR (1999-2007)
Ms Maclean decided to quit politics after stating she had "had enough", and has considered volunteering overseas or working in health or equal opportunities.
The former Dundee City Council leader and Holyrood committee convener, who represented Dundee West, caused short-lived controversy in the parliament's early days after admitted to having smoked cannabis.
She has maintained her backing of Labour and Jack McConnell but said politicians were increasingly "held in contempt by the public", despite the vast majority being genuine.
JOHN HOME ROBERTSON: LABOUR (1999-2007)
The East Lothian MSP was one of several Labour MPs who decided to make the move from Westminster to Holyrood in 1999.
He became deputy minister for rural affairs but really found himself in the hot seat on his appointment to the progress group overseeing the controversial Scottish Parliament building project.
It is understood he has been offered a seat in the House of Lords.
BRUCE McFEE: SNP (2003-2007)
Mr McFee stood in the Renfrewshire West seat for the 2003 election. He managed to win just over a quarter of the vote, and his list seat in Holyrood.
He served on the Scottish Parliament's local government and transport committee and has expressed a wish to be elected as a councillor.
The West of Scotland list MSP refused to support former SNP leader John Swinney in a leadership ballot in 2003, after claiming his position on independence had confused voters.
PHIL GALLIE: CONSERVATIVE (1999-2007)
The South of Scotland MSP missed out to David McLetchie in the race to lead the Scottish Conservative candidates group in 1998.
However, he won a list position in the first Holyrood election after narrowly losing the Ayr seat to Labour.
He said in 2002 that he would refuse to officially declare his long-standing membership of the Freemasons, claiming it did not impact on his actions in parliament.
The former MP, who once became stuck in a lift during a 2004 visit to the new Scottish Parliament complex, expressed a wish to seek election to the European Parliament.
JAMES DOUGLAS HAMILTON: CONSERVATIVE (1999-2007)
The Scots Tory education spokesman in Holyrood is credited with having charm and politeness - most who know him will share a fond anecdote or two from his long service in public office.
The former Tory Scottish Office minister lost his Westminster seat to Liberal Democrat Donald Gorrie in 1997.
The Lothians list MSP disclaimed an earldom in 1995 during his MP days and forfeited his right to a £500,000 inheritance to stay in parliament and help then Prime Minister John Major in a crucial European finance vote.
DONALD GORRIE: LIBERAL DEMOCRATS (1999-2007)
The Central Scotland list MSP has been one of Holyrood's more independent voices over the years and one of the arch critics of the costs of the Scottish Parliament building project.
The former MP incurred wrath from Labour after a comment that the late First Minister Donald Dewar may have regarded the building as a personal memorial.
A keen contributor to debates and always ready to scrutinise party policies, Jack McConnell jokingly said he had a knack for irritating other MSPs in the chamber.
JIM WALLACE: LIBERAL DEMOCRAT (1999-2007)
The Orkney MSP served as Deputy First Minister from devolution until 2005, when he stepped down as Scottish Liberal Democrat leader on a high after his party's General Election successes.
One of Holyrood's most widely respected parliamentarians, the former MP covered Scotland's top job on several occasions, including stepping in following the death of Donald Dewar and the resignation of Henry McLeish.
As justice minister, he was forced to perform a series of u-turns, with plans to ban smacking, close Peterhead jail and open up children's hearings to over-16s all dropped.
DENNIS CANAVAN: INDEPENDENT (1999-2007)
The ex-Labour MP was forced to stand for Holyrood in his own right after he failed to be selected as an official party candidate.
He later claimed the selection system to be rigged and "headed by mediocre stooges".
Popular with constituents and MSPs, the member for Falkirk West won recognition for his amendments to the parliament's landmark right-to-roam legislation to extend access to the Queen's estates.
He also stood for first minister four times and held the biggest majority in parliament.
He suffered the loss of two sons to cancer and a third, in March 2007, to motor neurone disease. Mr Canavan decided not to seek re-election after saying he had been taught a lesson in life's "real priorities".
BRIAN MONTEITH: INDEPENDENT (1999-2007)
The Mid Scotland and Fife MSP led the "Think Twice" campaign for a "no" vote in the 1997 devolution referendum before taking up his list seat as a Conservative at Holyrood.
He was seen as a colourful debater in parliament and served terms as convener of the audit committee and as the party's education and arts spokesman.
Mr Monteith resigned from the Scottish Tories in 2005 after admitting plotting against the then party leader David McLetchie, who later resigned, but wanted to see out his elected term as an independent.
GEORGE REID: OTHER (1999-2007)
The veteran Nationalist and ex-MP took Ochil from Labour in 2003 after serving as a Mid-Scotland and Fife list MSP.
He left SNP party politics to become the Scottish Parliament's presiding officer. Mr Reid quickly made moves to take the heat out of the Holyrood building project, while stressing his enthusiasm for the reform of parliamentary procedures.
As PO he won acclaim for his work to promote the parliament and Scottish devolved government on the international stage. He was also known for taking a tough line on MSPs misbehaving in the chamber.