Preface

The last three decades have seen an enormous surge of activity in the study of dwarf galaxies. To give a measure of that, the number of publications in the year 1981 containing both words “dwarf” and “galaxy” in the title was only 19. This number has grown almost monotonically over the following two decades, and in 2010 it was 243. As of 19.10.2011 already 238 publications on dwarf galaxies have been put in the preprint archive. The reason for this growing interest is quite obvious: advanced ground-based and space-born observatories allow to observe dwarf galaxies over a wide spectral window to an unprecedented level of detail. The advent of the HST has permitted sharp insights into the formation history of stellar populations of dwarf galaxies in the Local Group and its close vicinity back to the epoch of the cosmic reionization. Early-type dwarfs in galaxy clusters, at first glance featureless and deceptively simple, now turn out to have a rich “biography”, as witnessed by the variety of structural and kinematical patterns recently discovered in them. Galaxy clusters as gigantic cosmic factories of galaxy evolution are now being studied in considerable detail, unraveling spectacular dwarf galaxy transformation processes driven by the hot intra-cluster medium and the mutual interaction between thousands of galaxies. On the other hand, comparatively unevolved dwarfs residing close to the boundaries of voids suggest that the “cosmic clock” ticks slower in these largely unexplored pristine environments. The intriguing diversity of the dwarf galaxy population, further enriched by the discovery of ultra-faint and ultra-compact systems, and of tidal dwarf galaxies in the outskirts of colliding galaxy pairs, poses new challenges both to observers and theoreticians. The starburst phenomenon in low mass galaxies both in the nearby universe and out to intermediate redshift continues confronting us with fundamental yet poorly resolved questions. These pertain to, e.g. the origin of starbursts and their role on the dwarf galaxy buildup, the synchronization and spatial progression of star-forming activities within dwarfs, and the synthesis, dispersal and possible ejection of heavy elements during such violent episodes of dwarf galaxy evolution. The number of extremely metal-poor nearby star-forming dwarf galaxies has grown from about a dozen by the end of the past millennium to more than 70 in 2011. This