Hojlund has signed a five-year contract at Old Trafford and becomes the Red Devils' third summer signing after Mason Mount and goalkeeper Andre Onana.
The 20-year-old spent just one season in Serie A with Atalanta and scored nine goals in 32 league games.
Hojlund's record for Denmark is pretty impressive too, with six goals recorded in as many caps.
Before joining Atalanta last summer, Hojlund played for FC Copenhagen in his homeland and Sturm Graz in the Austrian Bundesliga.
“It is no secret that I have been a fan of this great club since I was a small boy and I dreamed of walking out at Old Trafford as a Manchester United player,” Højlund told the club website.
"I am incredibly excited by this opportunity to turn that dream into a reality, and I am determined to repay the faith that the club has shown in me. It is still early in my career, but I know that I am ready to make this step up and play with this group of world-class players.
"Once I had spoken to the manager, I knew that this environment would be perfect for my development; I am relishing the opportunity to work with one of the best coaches in the world. Under his guidance and support I know that I am capable of achieving great things together with my new teammates at this special club."
Manchester United manager Erik Ten Hag said of his new addition: "He is a real frontman. Very direct to the goal, very good presser, a physical presence. I think in the balance of this squad, we needed that, alongside Rashford, another player who is direct and can score a goal. That is all in his mind: he wants to score goals.
"I think he has huge potential. And now it's up to him first, to explore that and we will support him, all the coaches, the team. The team was waiting for a type like him. They will integrate him in the dressing room and in the pitch; they will help him.
"Finally, the player has to prove it. That is the character we need; we need hungry players and he is a player who is so determined to score goals, winning games and winning trophies."
