Both well-known and emerging viruses increasingly affect humans and cause disease, sometimes with devastating impact on society. The viruses present in the biosphere are the top predators in the life chain, virtually without enemies, except perhaps the immune system, and harsh environmental physicochemical conditions restricting their dissemination. We know a lot about viruses, but do we know enough? This series of reviews is dedicated to adenoviruses (AdVs), a family of nonenveloped DNA viruses occurring in vertebrates, including humans. AdVs have been the focus of intense research for more than 67 years. Besides causing disease, they have immensely contributed to the advance of life sciences and medicine over the past decades. Recently, AdVs have been widely used as vehicles in gene therapy and vaccination. They continue to provide fundamental insights into virus-host interactions in cells, tissues and organisms, as well as systems and metabolic networks. This special issue of FEBS Letters presents a unique collection of 23 state-of-theart review articles by leading adenovirologists. In this prelude, I present the chapters, which provide a solid basis for further exploring the rich heritage in adenovirus molecular cell biology, structural biology, genetics, immunology, gene therapy and epidemiology. I conclude with an essential discussion of six blind spots in adenovirology.Adenoviruses (AdVs) are nonenveloped, doublestranded DNA viruses of vertebrates. They are abundant in fish, amphibia, reptilia, birds and mammals, including humans. Currently, about 110 human adenovirus (HAdV) types and genotypes are known and classified into seven species (A-G). AdVs infect the respiratory organs, the eyes, the kidney, the gastrointestinal tract and blood cells. On a population scale, AdVs emerge unpredictable, and can cause human epidemics.The structure of the virion is related to phages of eubacteria and archaea, and is part of an evolutionary lineage comprising the internal membrane-bearing PRD1 phage of the tectiviridae infecting Gram-negative bacteria, paramecium bursaria chlorella virus infecting green algae, sulfolobus turreted icosahedral virus infecting archaea, as well as vaccinia virus, an attenuated form of the cowpox disease virus, related to variola virus causing small pox [1][2][3][4][5]. Both AdVs