Inclusionary zoning (IZ) requires or incentivizes residential developers to make a percentage of new units affordable to lower-income households — typically 10–25% of units, with affordability tied to area median income (AMI) and durations ranging from 30 years to perpetuity. IZ exists in hundreds of U.S. cities with widely varying designs: mandatory vs. voluntary, on-site vs. fee-in-lieu, with or without density bonuses.
Proponents argue IZ integrates affordable housing into market-rate developments, prevents concentrated poverty, and captures a share of land-value appreciation for public benefit. Well-designed IZ — with density bonuses, fee-in-lieu options, and predictable rules — can produce affordable units alongside new market-rate supply.
Critics — including some economists across the political spectrum — argue IZ acts as a tax on new construction that suppresses overall housing supply, raises market-rate prices, and ultimately produces few affordable units. They argue that broad-based subsidies (LIHTC, vouchers) or land-value taxation would produce affordable housing without suppressing market supply. Empirical research on IZ's net effect is contested and depends heavily on local-market conditions and program design.