According to the controlled demolition hypothesis, the World Trade Center was not destroyed by the planes that crashed into it as part of the September 11th attacks, nor by the fires that followed, but by explosives or other devices planted in the buildings in advance. Although an investigation by the National Institute of Standards and Technology (NIST) rejected the hypothesis as fundamentally lacking in evidence, it has become central theme for members of the 9/11 Truth Movement. The most detailed statements of the hypothesis have come from Steven E. Jones, Kevin Ryan, Jim Hoffman, David Ray Griffin and Webster Griffin Tarpley. In making their case, they often emphasize the collapse of 7 World Trade Center, which was not hit by a plane. Several organizations which associate skeptics of the known evidence of the collapse have been created; part of their focus being directed on criticizing NIST report.

Others, such as dental materials engineer Judy Wood, whose claims have been openly rejected by most other demolition hypothesis proponents, say that the observed damage to the twin towers and surrounding WTC buildings could only have been accomplished with some type of directed energy weapon, possibly space-based.

The idea of controlled demolition is normally presented as a hypothesis still to be tested, not a proven claim. Mainstream engineers, investigators, industry experts, and all informed sources dismiss it as a conspiracy theory.