It is well documented that bridges offer substantial amounts of roost habitat for millions of bats. Many bridges provide temporal and environmental stability, which makes them highly suitable for use by bats during seasonal periods of bat activity and in some cases also during winter. Bridges are usually large structures that can support large colonies, often with a variety of roost features and characteristics that make them attractive to multi-species assemblages. Bats that use bridges vary in size as well as preference of roost feature characteristics. The author provides design criteria, including bridge- and species-specific details, of successfully-occupied replacement, in-structure roost habitat, which he has developed and refined over many years for bridges in California. The author also discusses the iterative, cooperative processes involved in working with bridge engineers and architects to incorporate important biological requirements into construction plans and completed bridges.