The quadratic assignment problem (QAP) is a classical combinatorial optimization problem with numerous applications in facility location, scheduling, manufacturing, VLSI design, statistical data analysis, etc. The QAP is an extremely hard problem from both theoretical and practical points of view: 1) The QAP is NP-hard to solve to optimality and to approximate within a constant approximation ratio, and 2) QAP instances of size larger than 22 are still considered intractable. Hence, the QAP is in effect a problem that has yet to be solved. This volume presents a general overview of the most studied aspects of the QAP, as well as outlining a number of research directions which currently seem to be promising. The book gives a systematic presentation of various results scattered in the literature, such as: bounding techniques and exact solution methods, linearisations, heuristic approaches and computational complexity. Some more recent research directions discussed in detail in the book are the asymptotic behaviour of the QAP and restricted versions of the problem: in particular, polynomially solvable and provably hard cases of the QAP. Audience: This volume will be of interest to researchers and students interested in the quadratic assignment problem and to practitioners who face the QAP and wish to better understand this problem in its inherent complexity.