The September 11 attacks (also referred to as 9/11)[nb 1] were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda on the United States on the morning of Tuesday, September 11, 2001. The attacks killed 2,996 people and injured over 6,000 others and caused at least $10 billion in property and infrastructure damage[2][3] and $3 trillion in total costs.[4]