Hook was introduced to the Perpignan crowd during half-time against Castres on Saturday and the French club's president Paul Goze reckons he is Europe's finest.
"I am very happy to welcome James," said Goze.
"For me he's the best player in Europe and, without diminishing the roles of the other players, the midfield triangle of Hook, Maxime Mermoz and David Marty is special."
Hook has signed a three-year deal with the Catalan giants and is looking forward to joining their ranks, even though they have missed out on Heineken Cup qualification.
"Perpignan is an exciting challenge for me after seven seasons at Ospreys," added 25-year-old Hook.
"I've always enjoyed playing French sides in the European Cup. When we played Perpignan two seasons ago, I was impressed by the atmosphere here. The fans are incredible.
"Perpignan are a solid side, powerful up front, a seasoned European Cup outfit and who are one of the best at that level. I had been contacted by other French clubs, but Perpignan was my first choice.
"It is a shame that there will not be any European Cup campaign, but the Top 14 offers week-in week-out duels of the highest level."