Under a universalist model of public housing (e.g., Vienna), the state builds and retains a large housing stock open to most of the population, including the middle class, with secure tenancies and mixed-income estates. Under a residualist model (e.g., the UK, US, and Norway), public housing is a smaller safety net reserved through means testing for the poorest households, with everyone else housed by the private market, sometimes aided by vouchers or allowances.