Subprime mortgage lending is controversial. Its critics see excessive prices, unfair terms and "predatory" practices. Proponents see a much narrower set of problems. Legislative and regulatory solutions to perceive problems are being implemented piecemeal across states and even local...

We describe a rational expectations model in which speculative bubbles in house prices can emerge. Within this model both speculators and their lenders use interest-only mortgages (IOs) rather than traditional mortgages when there is a bubble. Absent a bubble, there is no tendency for IOs to be...