It's one of the top honours in rugby union and Sam has become only the second player in Lions' history to lead the team into two tours, having captained the victorious tour of Australia in 2013. Martin Johnson was the first to achieve that in 1997 and 2001 - Lions tours go all the way back to 1888.
Coach Warren Gatland has named a 41-man squad for a 10-match tour that begins on June 3 and includes three Test matches against the All Blacks on June 24 (Auckland), July 1 (Wellington) and July 8 (Auckland).
Below: Sam at the Lane with Cliff Jones and Alan Mullery in February, 2015
Speaking on Sky Sports just after the announcement, Sam said: "It's hard to put into words. Even four years later, the 2013 tour hasn't really sunk in, to be honest.
"We had a dinner last night with all the ex-captains from previous Lions' tours and it's only when you are sat down on that table and you see the company you are with that you realise what you are doing.
"That hit home to how big a deal it is, especially this time around with New Zealand, arguably the toughest tour. It's an amazing challenge and an amazing opportunity."
Below: Sam with coach Warren Gatland at today's announcement
Sam became the first Welshman to captain the Lions since Phil Bennett in 1977 when he took the armband in 2013. He performed superbly as Lions won the first Test 23-21 before narrowly losing the second 16-15. He was injured for the third Test where Lions ran out 41-16 winners to clinch the 2-1 series victory.
Capped 75 times by Wales, Sam first represented his country in 2009. He captained Wales for the first time in 2010 and led them at the 2011 World Cup, where they reached the semi-finals. Wales then clinched the Six Nations' Grand Slam (winning all five matches) in 2012, retaining the title in 2013.
LIONS IN NEW ZEALAND - 2017
Game 1: Saturday, June 3 v Provincial Union Team in Whangarei
Game 2: Wednesday, June 7 v Blues in Auckland
Game 3: Saturday, June 10 v Crusaders in Christchurch
Game 4: Tuesday, June 13 v Highlanders in Dunedin
Game 5: Saturday, June 17 v Maori All Blacks in Rotorua
Game 6: Tuesday, June 20 v Chiefs in Hamilton
Game 7: Saturday, June 24 v All Blacks in Auckland
Game 8: Tuesday, June 27 v Hurricanes in Wellington
Game 9: Saturday, July 1 v All Blacks in Wellington
Game 10: Saturday, July 8 v All Blacks in Auckland