Culverts are sometimes mentioned in the context of anthropogenic structures providing bat roosting habitat; however, there is a paucity of available information about these roosts. Data collected throughout Southern California over a 15-year period show that at least eleven bat species roost in various culvert types; these include concrete box, arch, and pipe culverts as well as corrugated metal pipe culverts. Occupied culverts are found in a variety of habitats, including heavily urbanized landscapes, and bats have been observed day roosting (including maternity roosting), night roosting, and even mating within culvert structures. Features used by bats in culverts vary widely and can include overlap joints, expansion joints, manhole access shafts, drainage pipes, open surfaces, and bird nests. Misconceptions about what constitutes suitable roosting habitat in culverts can result in these structures being overlooked during environmental review, and consequently impacts to bats roosting in culverts are often not adequately mitigated. Bats roosting in these structures are also vulnerable to disturbance from human entry, vandalism, and increases in artificial light at night (ALAN) in adjacent areas. Because roosting habitat is a limited and declining resource for bats, overlooking culverts or less-commonly encountered features in culverts as roosts can have profound conservation implications.