  This is a chapter in a book \emph{Quantum Error Correction} edited by D. A.
Lidar and T. A. Brun, and published by Cambridge University Press (2013)\\
(http://www.cambridge.org/us/academic/subjects/physics/quantum-physics-quantum-information-and-quantum-computation/quantum-error-correction)\\
presenting the author's view on feasibility of fault-tolerant quantum
information processing.
