In the United States, where approximately one-third of U.S. households rent rather than own their homes, rents since 2000 have become increasingly unaffordable for low- and middle-income families in virtually every U.S. metropolitan area. This trend is especially concerning because rents were already unaffordable for a large share of low-income households in the 1990s. Our analysis shows that, in that decade, even in a best-case scenario in which all renters hypothetically rented homes perfectly matched to their income e.g., a family at the 20th percentile of income rented a home that is at the 20th percentile of the local rental price distribution, and so on—the average low-income household in 226 out of the 238 largest metropolitan statistical areas (MSAs) in the United States still needed to pay more than 30 percent of its income a common metric of affordability.