Homelessness is analyzed systemically in terms of the "low-income housing ratio"—the number of households living below the poverty line divided by the number of affordable housing units available. When there is a shortage of affordable low-cost housing units, some low-income households pay more than they can afford for housing and others double up with friends or family. However, once those households that can pay more or double up have done so, if there are still more low-income households than there are low-cost housing units, homelessness will inevitably result. This will be true regardless of the characteristics of the households that become homeless. Thus, mental health approaches that treat the individual without changing the overall low-income housing ratio will be ineffective in reducing homelessness, as will programs providing only emergency shelter or transitional housing. Only those programs that reduce poverty or increase the supply of affordable housing will be effective in decreasing the total number of homeless families in the United States.