This is a review of the available knowledge on nuclear behavior of the mycelium within polypore genera (Agaricomycetes, Basidiomycota). Information on 68 genera showed that nuclear behavior is a distinct and consistent feature at genus level and can be coupled with phylogenetic differentiation. The sole exception was found in Polyporus, where different species with normal, heterocytic and astatocoenocytic nuclear behaviors were found. Of the 68 genera treated 41 (60.3%) displayed a normal nuclear behavior, nine (13.2%) were heterocytic, nine (13.2%) were astatocoenocytic and another eight (11.8%) were holocoenocytic. In 95% of the genera a unique compatibility system was found, with the exceptions of Antrodia, which includes both homothallic and bipolar species all associated with a normal nuclear behavior, and Spongipellis, in which bipolar and tetrapolar species are found, all displaying an astatocoenocytic nuclear behavior. Normal and heterocytic nuclear behaviors were associated mostly with tetrapolarity, astatocoenocity was associated mostly with bipolarity, and holocoenocity was associated with either bipolarity or purported homothallism. The combination of nuclear behavior with mating system and brown or white rot capability appeared as a strong feature characterizing and distinguishing the genera of polypores, each combination being valuable to differentiate between apparently related genera, as is supported by phylogenetic studies. Several examples are presented to support this idea, as well as the cases of species that are problematic to this concept. Poroid genera of Hymenochaetaceae were treated apart because of the lack of knowledge regarding their nuclear behavior. In addition new information on the sexuality and/or nuclear behavior of 15 polyporoid taxa is given.