Over the past 30 years the rapid development of surface science techniques has led to remarkable progress in the understanding of the phenomenon catalysis, which is a complex system of various processes. Catalysis can generally be divided into four interrelated processes: adsorption, desorption, surface and subsurface diffusion, and interaction between coadsorbed atoms, molecules, and molecular fragments. It has been recognized that any foreign adsorbed species changes the local surface properties. In milder cases the adspecies modify the electronic structure of the substrate surface atoms with negligible changes in their equilibrium positions. In more severe cases creation of more suitable surface sites is required, which results in a completely changed substrate surface structure. That is why structural variations of the working catalyst surface, induced by the reaction participants, occur quite frequently and can result in nonlinear dynamics and kinetic oscillations.1-3 A real catalyst surface consists of “microsurfaces” of various crystallographic orientations. Going from lowto high-index faces the number of the nearestneighbor broken bonds increases, resulting in a higher surface free energy. This makes the higher index planes less resistive toward restructuring in the presence of strongly bound adsorbates. It appears that for a great number of surface reactions the higher index planes exert a higher activity and can be classified as preferred faces for the catalytic reactions. Hence, the possible structural variations Dr. Maya Kiskinova began her research in surface chemistry and catalysis as a diploma student at the University of Sofia where she got her M.S. in 1972. As a graduate student she continued her studies on chemisorption on metals. She got her Ph.D. in Physical Chemistry in 1977 and her Sc.D. degree in 1989 in the Bulgarian Academy of Sciences, where she worked until 1990. During the period 1980−1990 she worked for long periods as a visiting scientist at the National Bureau of Standards and at the University of Pittsburgh in the United States and at the Scientific Center of Juelich in Germany. Presently, she is a group leader at the ELETTRA Laboratory in Sincrotrone-Trieste (Italy), a position which she has held from 1991. Her research activity covers studies on single-crystal metals and semiconductors, thin films, and oxide and silicide interfaces using wide range of surface sensitive spectroscopies and local probe techniques. Her research is focused on understanding processes involved in the structural and chemical transformations of chemisorbed systems on model metal catalysts and their relation to surface reactivity and in the chemical modifications of semiconductor surfaces. 1431 Chem. Rev. 1996, 96, 1431−1447