On the 10-year anniversary of 9/11, celebrities including Lady Gaga and Nas look back on how the world was changed in a new campaign in support of the 9/11 Day Observance. The “I Will” PSAs were created by Viacom to encourage all Americans to remember those lost by doing good deeds, supporting charitable causes, or volunteering in their communities.

“What will you do?” ask the familiar faces in the television spot, which will air across Viacom channels.

“We were in disbelief,” said New York native Gaga as she recalled the tragic events, while Nas added, “No one was ready for 9/11 when it happened. … I will remember the people that we lost.”