"As soon as I knew they were interested in me I knew there was only one club that I wanted to sign for and thankfully it has now happened," said Riera.
"I know I will have to work very hard to get into the team because there are a lot of good players here but that is a challenge I am looking forward to.
"It feels really good to be a Liverpool player and I am really happy to be at this club.
"I am looking forward to working with the manager and the players."