The relation between the electronic structure of platinum metallic aggregates and their selectivity is discussed. A correlation is underlined between the energy of the d-band center, epsilon(d), and the catalytic reactions such as hydrocarbon isomerization. Similar behavior appears when CO chemisorption on a platinum surface is compared with activity in alkane isomerization. This relationship can be used to interpret the changes in the mechanisms observed in acid catalysis, with bimetallic systems, and with catalysts treated by microwaves. (C) 2003 Elsevier Science (USA). All rights reserved.