The Wall Street bombing occurred at 12:01 pm on Thursday, September 16, 1920, in the Financial District of Manhattan, New York City. The blast killed thirty people immediately, and another ten died later of wounds sustained in the blast. There were 143 seriously injured, and the total number of injured was in the hundreds.

The bombing was never solved, although investigators and historians believe it was carried out by Galleanists (Italian anarchists), a group responsible for a series of bombings the previous year. The attack was related to postwar social unrest, labor struggles, and anti-capitalist agitation in the United States.

The Wall Street bomb killed more people than the 1910 bombing of the Los Angeles Times, which was the deadliest act of terrorism on U.S. soil up to that point.

At noon, a horse-drawn wagon passed by lunchtime crowds on Wall Street and stopped across the street from the headquarters of the J.P. Morgan & Co. bank at 23 Wall Street, on the Financial District's busiest corner. Inside the wagon, 100 pounds (45 kg) of dynamite with 500 pounds (230 kg) of heavy, cast-iron sash weights exploded in a timer-set detonation,  sending the weights tearing through the air. The horse and wagon were blasted into small fragments, but the driver was believed to have left the vehicle and escaped.

The 40 fatalities were mostly young people who worked as messengers, stenographers, clerks, and brokers. Many of the wounded suffered severe injuries.  The bomb caused more than US $2 million ($27.1 million today) in property damage and destroyed most of the interior spaces of the Morgan building.

Within one minute of the explosion, William H. Remick, president of the New York Stock Exchange (NYSE), suspended trading in order to prevent a panic. Outside, rescuers worked feverishly to transport the wounded to the hospital. James Saul, a 17-year-old messenger, commandeered a parked car and transported 30 injured people to an area hospital. Police officers rushed to the scene, performed first aid, and appropriated all nearby automobiles as emergency transport vehicles.