Last week saw Simon Cowell kick things off in Malibu with the Girls.
This weekend, the Boys join Louis Tomlinson in Ibiza, while over in LA the Groups perform for Robbie Williams, and the Overs hope to impress Ayda.
Joining Ayda will be two special guest judges, American Idol star Adam Lambert and former X Factor winner Leona Lewis.
Giving her tips to the contestants, Leona told the Daily Mail from America: "My advice would be to take in each moment and really be in it. Especially with some of the performances by the overs, I saw that they were in their head a lot and not in the moment.
"It’s so important, especially when I look back at what I did on the show. It does go by so fast. You really have to enjoy it and put your best foot forward. You must know what you’re doing and practice, but as soon as you get up on that stage you have to let it all go and really enjoy it."
Speaking about the experience as a guest judge, Leona said: "It’s been really great. I’ve really enjoyed the performances and I got to be at Simon’s house as well with the girls.
"So I got a double whammy, which was great! I love the overs because they have so much to give. They have a lot riding on getting through and that really comes across in their performances. You just feel the gravity of how much they want it. So it was a very different experience seeing the overs perform compared to the girls.
Meanwhile, Adam said: "It’s not easy, but I think at this point everyone knows what’s going on and they just want to help.
"I think having hung out with Simon at his place and now with Ayda and Robbie, they are seeing these people come to the show with dreams and a mission, or something to prove to themselves, their family or the world.
"I think at the end of the day the criticism is usually always constructive, I think the contestants know that."
Adam added: "I’ve had fun today helping Ayda figure out who she’s going to say yes and no to, that’s the sad part, saying no. I was really impressed with the talent, actually.
"Some of the contestants were very surprising, particularly Danny. I wouldn’t have expected that level of talent from him, for no particular reason, I just wasn’t ready for it, it caught me off guard. He was amazing!"
Elsewhere, Liam Payne and Nile Rodgers will join Louis Tomlinson while Robbie will team up with David Walliams.
The X Factor 2018 airs tonight (Sunday, October 14) at 8PM on ITV.