The fall of the Twin Towers of the WTC has been the subject of a series of expert discussions on the mechanism by which the fall took place, and especially its speed. The official NIST report states the following: "The release of potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse ensued." But how, then, is the collapse itself supposed to occur? With what acceleration? Is the fall of the upper floors supposed to accelerate or should it decelerate and subsequently stop due to the resistance provided by the columns below, and other factors? These are issues that the NIST report does not deal with but which are discussed in this book. The authors were indeed inspired by the fall of the WTC's Twin Towers, but the book is devoted to the dynamics of the collapse of high-rise buildings in general. In line with the conclusions of the NIST report, the authors assume that collapse was initiated by the loss of stability of the columns in one or more floors of the high-rise building due to fire or another triggering factor. This book deals with dynamics of collapse itself.