The 24-year-old has admitted that his compatriot and Belgium team-mate played a major role in his decision to sign for the Rojiblancos on Monday
The 24-year-old sealed a €7 million move to the Spanish capital from Ajax on Monday, signing a four-year deal with the Rojiblancos.
And Alderweireld says that his Belgium team-mate - who is on loan from Chelsea - sold the idea of life with Atletico to him.
The centre-back told the club's official website: "I said Atletico were interested in me and he [Courtois] told me how great it is, this team and its fans.
"He advised me to come because he is very happy here."
The Belgian, who made 128 Eredivisie appearances for Ajax, could be handed his debut by coach Diego Simeone in the Liga meeting with Almeria on September 13.