The social welfare system of the United States provides income maintenance through multiple programs that fall into two major groups: (1) means-tested programs that are targeted, by and large, on particular demographic groups and/or respond to specific needs; and (2) social insurance programs for which eligibility depends on prior contributions and/or work history, with the amount of benefits typically related to prior earnings. Under the rules and regulations of these programs, individuals and households can often qualify for and, if they choose, participate in more than one assistance program. Previous research on participation in assistance programs at a point in time, for which the 1979 Income Survey Development Program (ISDP) Research Panel (e.g., MacDonald, 1983; Weinberg, 1985) and the Survey of Income and Program Participation (SIPP) (e.g., McMillen, 1985; Falk and Richardson, 1985; Weinberg, 1986; Long, 1988) were used, has shown that a substantial amount of multiple program participation does occur. In particular, Weinberg (1986) found that multiple program participation was the norm in 1984: 76 percent of all families and unrelated individuals participating in at least one assistance program, received benefits from two or more of the eleven programs studied.