Background for the civil engineering design is given, and failure possibilities are provided. Various structural components, including the foundation slurry walls, the design of the column support system, and the performance of the floors are briefly described. The 110-story Twin Towers were constructed 30 years ago and utilized the latest engineering principles; they were stable, and workers as well as visitors often commented that the upper floors were comfortable and any sway was not noticeable during storms. © ASCE.