The isomerization of alkanes into corresponding branched isomers is one of the important processes in petroleum refining. Though the so-called bifunctional catalysts are used in industrial processes, the better catalysts are still sought for the improvement of the catalytic performance. The catalysts used in industrial processes and those of academic interest are described with emphasis on the mechanistic aspect. The catalysts include Pt supported on solid acids, sulfated zirconia, tungsten oxide supported on zirconia, oxycarbides of tungsten and molybdenum, and partially reduced MoO3. The mechanism of the isomerization over each catalytic system is described. The role of transition metals and hydrogen in bifunctional catalysts and the controversial mechanisms of alkane isomerization over sulfated zirconia are discussed in detail. Finally, recent development of the computational modeling and quantum mechanical calculations on alkanes activation and their transformations over zeolites are discussed with respect to the role of acid sites in the isomerization. (C) 2003 Elsevier Science B.V. All rights reserved.