EuroTrip begins with the main character Scott Thomas, known as Scotty, being dumped by his girlfriend Fiona at his high school graduation, in front of his parents and filmed on camcorder. Devastated, he e-mails the happenings to his German pen pal Mieke, which he mistakenly pronounces as "Mike" during which his friend, Cooper Harris, quips about all people on the Internet being gay men looking for sex.

They decide to go to a party to prove that Fiona won't stop him enjoying graduation, but they arrive to find that Fiona has been having sex with the lead singer of the college band (Matt Damon), and are then treated to a performance of the song "Scotty Doesn't Know", in which every detail of the lewd affair is revealed with an accompanying explanation of why Scotty didn't know about it.

Drunk and angry, Scott arrives home and receives an e-mail reply from "Mike", who says "he" is sorry for all that has happened to Scott, and wants to arrange a meeting in order to make him feel better. Scott replies by telling Mieke "he" is a sick German freak, resonating on his friend Cooper's earlier comment warning him about Internet relationships.

The next day Scott's brother Bert explains to him that "Mieke" in German is not "Mike" as Scott thought, but actually a name similar to "Michelle" in the English language. "No, retardo. That's not "Mike", it's Mieke, a common German girl's name, similar to our Michelle". Realizing his mistake, and that he has feelings for her, he tries desperately to e-mail Mieke again, only to find she had blocked his address. He resolves to travel to Germany, to fix the situation and confront her face-to-face. He tells his plans to Cooper, after which they plan to travel to Germany together.