Started in 1999, initially known as Independent Days Festival, it hosted as headliners some of the most important names in international music such as: Arcade Fire, Arctic Monkeys, Blink 182, Green Day, Imagine Dragons, Justin Bieber, Kasabian, Liam Gallagher, Linkin Park, Muse, Nine Inch Nails, Pearl Jam, Placebo, Queens Of The Stone Age, Radiohead, Sigur Ros, Sonic Youth, The Killers, The Offspring, Tool, Velvet Revolver and many others.

To date, I-Days holds the record for paying people at an Italian festival with over 210,000 attendees at the 2017 edition held at the Monza Park – Autodromo Nazionale.