Xana, obsessed with world domination, has taken over the supercomputer in charge of Lyoko, which he also dominates. Xana attacks the real world by activating towers (usually one at a time), which act as links to the real world. If the group is able to get Aelita to the activated tower(s) out of the more than forty scattered about Lyoko's four main regions, she can deactivate the tower(s) and neutralize Xana's attack on the real world; then they can use the supercomputer to return to the past, leaving no one except themselves to remember any of the events that transpired. To complicate the situation, they must do this while ensuring their classmates and teachers are not killed (as going back in time cannot bring back the dead), and deal with the many clashes of personality at the same time.

• The official Code Lyoko website.
• MoonScoop, the distribution company for the program.
• Code Lyoko – The Web Site, in English, French, and Spanish; a very extensive fan site. It appears to have input from Sophie Decroisette, the director of writing, on Code Lyoko.
• Codelyoko.fr, an extensive fansite with clips, episode guides, and galleries, among other things.
• The personal website of Frédéic Perrin, lead background painter for Code Lyoko. Contains a gallery of production artwork.