A rental real estate enterprise is defined, for purposes of the safe harbor, as an interest in real property held for the production of rents. A rental real estate enterprise may consist of multiple properties. The interest must be held directly or through a disregarded entity. Taxpayers either must treat each property held for the production of rents as a separate enterprise or must treat all similar properties held for the production of rents as a single enterprise. Commercial and residential real estate cannot be combined in the same enterprise.