Al said: "It's a privilege to play for Glasgow Warriors and I'm honoured to be captain of this club.
"Over the next three or four years I have one goal and that's to help this club win silverware. There is a strong squad and work ethic here and I want to be at the forefront of the push for success.
"Iím still keen to develop as a player and learn from the coaches at Glasgow. I'm still working hard at my game, still trying to improve and I have more to give to the Warriors.
"We have been shaping up over the last two or three seasons to do something special for the game in Scotland and compete with the best teams in Europe.
ďWinning a trophy against these sides is something I desperately want to happen for the game of rugby in Glasgow."
Glasgow Warriors head coach, Gregor Townsend, said: "Alastair embodies what the Warriors are all about and he will be one of the key drivers of our success in the years to come.
ďAl is an outstanding leader and ambassador for the club, but itís his on-field performances that have earned him the reward of this contract extension.
ďHe is one of the best lineout forwards in the game right now and has been a major part of our strong scrummaging displays this year.
ďLike any player in our squad there are areas he needs to keep working on to improve but Iíve been impressed with his low tackling and ball carrying this season. Iím delighted he has committed his future to the club."
A former pupil of Bishopbriggs High School, Al was part of the Glasgow Thistles squad that toured New Zealand in 2000.
Al has represented Scotland at under-19 and under-21 levels and remains attached to the Scottish Institute of Sport.
He played his club rugby initially with Allan Glen's before moving to Stirling County. His talent was noticed at Bridgehaugh and, with help from the Scottish Institute of Sport.
Al swiftly progressed through national age-group squads to the Edinburgh side, where he replaced Nathan Hines as a regular alongside Scott Murray.
Al was given his first full international chance by Matt Williams, one of a clutch of promising youngsters taken on tour to Australia and New Zealand in 2004.
His senior Scotland debut was in the non-cap tour game against Queensland Reds on the 2004 summer tour of Australia.
He followed that by coming on as a replacement in the games against New South Wales Country and New South Wales Waratahs.
Al went on to gain his first cap against Australia at Murrayfield in the opening match of the 2004 Abbey Autumn Tests, coming on as a replacement.
He made such a favourable impression on his arrival in the Glasgow squad that he was appointed captain.
Al made his first competitive appearance as captain against Newport Gwent Dragons at Hughenden on the Magners League's opening day.