Avian reoviruses are important pathogens that cause considerable losses to the poultry industry, but they have been poorly characterized at the molecular level in the past, mostly because they have been considered to be very similar to the well-studied mammalian reoviruses. Studies performed over the last 20 years have revealed that avian reoviruses have unique properties and activities, different to those displayed by their mammalian counterparts, and of considerable interest to molecular virologists. Notably, the avian reovirus S1 gene is unique, in that it is a functional tricistronic gene that possesses three out-of-phase and partially overlapping open reading frames; the identification of the mechanisms that govern the initiation of translation of the three S1 cistrons, and the study of the properties and activities displayed by their encoded proteins, are particularly interesting areas of research. For instance, avian reoviruses are one of the few nonenveloped viruses that cause cell-cell fusion, and their fusogenic phenotype has been associated with a nonstructural 10 kDa transmembrane protein, which is expressed by the second cistron of the S1 gene; the small size of this atypical fusion protein offers an interesting model for studying the mechanisms of cell-cell fusion and for identifying fusogenic domains. Finally, avian reoviruses are highly resistant to interferon, and therefore they may be useful for investigating the mechanisms and strategies that viruses utilize to counteract the antiviral actions of interferons.