The research interests of Professor Petrosian have been in two broad areas of high energy astrophysics and cosmology. The former area includes studies of acceleration, transport and radiation of non-thermal particles, developed primarily for application to solar flares. This works has also found application in variety of other astrophysical sources including accretion disks, Gamma-ray bursts and Clusters of Galaxies. The work in cosmology is focused on evolution of galaxies and quasars (and AGNs in general), and in luminous arcs in clusters of galaxies (of which he is a co-discoverer) and gravitational lensing. Another interest has been in the area of statistical methods relevant to analysis of astronomical data. This work is carried out in collaboration with B. Efron of the Statistics Department at Stanford has been concentrated on development of new non-parametric methods for determination of distribution of astronomical sources from truncated data.