Across the United States, many urban, suburban, and even rural neighborhoods are experiencing dramatic transformations. Parking lots, underused commercial properties, and former industrial sites are being replaced by condominiums, apartments, townhouses, and small-lot single-family homes. These examples of residential infill—or building new homes in previously developed areas—can help to expand housing choices, make neighborhoods livelier, increase the tax base, safeguard rural landscapes, reduce infrastructure costs, and protect natural resources. Infill can also provide significant environmental benefits when compared with conventional greenfield1 suburban development—including reduced transportation emissions from new residents and reduced stormwater pollution washing off of new roadways and other paved surfaces.