Overall, the size of the Section 8 program—that is, the combined number of authorized vouchers and project-based units—increased annually, from 2.93 million in 1998 to 3.36 million in 2004, or 15 percent during the period. This growth resulted exclusively from the authorization of additional vouchers; the number of project-based units actually declined. Specifically, the number of authorized vouchers rose from about 1.60 million in 1998 to 2.09 million in 2004, a 31 percent increase. At the same time, the number of authorized project-based units fell from 1.33 million to 1.27 million, a 5 percent decrease, primarily because property owners and HUD decided not to renew some project-based contracts. HUD generally provided vouchers to households in project-based units for which contracts were not renewed so that these households could continue receiving rental assistance. These “tenant protection” vouchers, including those provided to households no longer receiving assistance under other HUD programs, accounted for 42 percent of the increase in the number of vouchers from 1998 through 2004.