Andrew Strauss has stepped down as England Test captain and retired from professional cricket.
Strauss, 35, made the decision in the wake of the 2-0 Test series loss to South Africa this summer, which saw the Proteas replace England at the top of the world rankings.
Alastair Cook, who already leads England in ODIs, will take over as Test captain.
"After much thought over the last few weeks, I have decided to step down as England Test captain and announce my retirement from all forms of cricket," said Strauss.
"It has clearly been a tough decision to make, but I believe that it is both in the best interests of the England cricket team and myself to step down at this stage."
He was captain in exactly half of his 100 Tests, leading his country to 24 wins, 15 draws and 11 defeats.
As an opening batsman, Strauss scored 7,037 runs at an average of 40.91, including 21 centuries, the first of which came on debut against New Zealand in 2004.
Strauss took the helm in February 2009 after the double sacking of Kevin Pietersen as captain and Peter Moores as coach.
Alongside team director Andy Flower, he oversaw a period of sustained success that included Ashes wins at home and abroad.
England went top of the Test rankings last year after their series win over India at home but have since struggled to justify that status.
They have since lost six of their 12 Tests, including series defeats to Pakistan and South Africa.
The latter of those was overshadowed by a row that saw Kevin Pietersen dropped for the final Test after he admitted sending "provocative" text messages - reportedly including criticisms of Strauss' leadership - to South Africa's players.
"There are too many people who have helped me on this incredible journey to mention them all by name, but I would like to thank all the Middlesex and England players I have played alongside, as well as the phenomenal coaches and support staff with whom I have been fortunate enough to work," added Strauss.
"Particular mention has to go to Andy Flower and Duncan Fletcher in that regard. It would also be remiss of me not to thank Middlesex County Cricket Club, the ECB and the PCA for their support and guidance over the years.
"No one can play international cricket for any length of time without having an incredibly strong support network around them, and I would like to take this opportunity to thank my family for going through it all alongside me over the course of my England career.
"I am extremely proud of everything I have achieved as a cricketer, and I have found myself very fortunate to play in an era when some of English cricket's greatest moments have occurred. I have loved every minute of it. All that remains is for me to wish Andy, Alastair and the rest of the team the very best for the coming months. I will be an interested spectator."
Cook paid triubute to Strauss and admitted he will be a big loss to team.
"Andrew's contribution to England cricket in recent years is evident to everyone who follows the sport but only those of us who have been lucky enough to share a dressing room with him are fully aware of his immense contribution to our success," said Cook.
"He has been a fantastic captain, has led from the front for three and a half years and is a true ambassador for the game.
"To have played 100 Tests for your country is a phenomenal achievement and I want to congratulate him on a superb career. I know this can't have been an easy decision for him and everyone in the dressing room will be sad to see him go.
"I'm very excited by this new challenge, it is a huge honour to be appointed Test captain and am very much looking forward to captaining the side in India this winter and beyond but my immediate focus is on this current NatWest one day series. Once the series is over I will turn my attention to the Test captaincy and building on the work Andrew has started."
England and Wales Cricket Board chief executive David Collier added: "On behalf of the ECB and everyone involved in cricket I'd like to thank Andrew Strauss for his outstanding contribution to the game.
"Andrew has been a highly successful captain and opening batsman for Middlesex and England who will be remembered for leading the side to two Ashes victories and to the top of the Test rankings.
"He has shown tremendous integrity, dedication and commitment both on and off the field and under his leadership the side has grown immeasurably and reached new levels of professionalism.
"Andrew's calmness and authority when dealing with some of the most difficult moments in our sport in recent times should be applauded and I have no doubt that his contribution as an ambassador for the game will be recognised by anyone who has had an opportunity to spend time with him.
"His legacy within the game will be felt for many years to come and we now need to continue to build on the progress we have made under his leadership."
Is it the right time for Andrew Strauss to quit as England Test captain?