The midfielder has completed his move from the South Coast to last season's Premier League runners-up.
Lallana thanked his old club during an interview with LFC TV for the time he spent with the Saints but has said he is ready for a new challenge at Anfield with the aim of winning trophies at the club, after signing a long-term contract.
The 26-year-old will wear the number 20 shirt for the Reds and will link up with Rickie Lambert, who he also spent time with at Southampton. Lambert completed his move to Liverpool prior to the World Cup.
Here are some photos of Lallana unveiled as Liverpool player:
Liverpool FC (@LFC) July 1, 2014
Prior to his transfer, Lallana spoke of his desire to play in the Champions League having been a spectator at a couple of games in the past, and is likely to line up in Europe's premier club competition for the Reds this season.
But before that, he could make his competitive debut against the club he signed from, Southampton, on August 16 in the Premier League at Anfield, as the Reds look to mount a challenge to go one better in the Premier League title race this time around.
Manager Brendan Rodgers seems happy with his signing, telling the Liverpool website: "Adam is aware there will be great competition for places at this club and he is hungry to improve further. We are confident he will fit perfectly with the culture we have at Liverpool."