23-year-old Lammers has joined the Italian side on a long-term contract for a reported fee of €10m.
Semaforo verde! 🚦 Sam #Lammers è nerazzurro! Welkom, Sam! 👋🏼🇳🇱
All right, green light! 😁 Sam Lammers is a new #Atalanta player! Welcome, Sam! 🖤💙
— Atalanta B.C. (@Atalanta_BC) September 22, 2020
Lammers played for PSV from 2010, making his first team debut in 2016 at the age of 19.
In total, he made 29 appearances for his boyhood club, scoring six goals.
PSV sporting director John de Jong admitted the club wanted to keep Lammers, but he was set on a move to Atalanta.
Head coach Roger Schmidt already has a replacement after PSV secured the signing of Eran Zahavi over the weekend.