Mentally ill people turned out of institutions, crack-cocaine use on the rise, more poverty, public housing a shambles: as attempts to explain homelessness multiply so do the homeless - and we still don't know why. This is a story about markets, not about the bad habits or pathology of individuals. One perplexing fact is that, though homelessness in the past occurred during economic depressions, the current wave started in the 1980s, a time of relative prosperity. As Brendan O'Flaherty points out, this trend has been accompanied by others just as unexpected: rising rents for poor people and continued housing abandonment. These are among the many facts that O'Flaherty collected and analyzed in order to account for the new homelessness. Focused on six cities (New York, Newark, Chacago, Toronto, London and Hamburg), his studies also document the differing rates of homelessness in North America and Europe, and from one city to the next, as well as changes in the composition of homeless populations. O'Flaherty shows that the conflicting observations begin to make sense when we see the new homelessness as a response to change in the housing market, linked to a widening gap in the incomes of rich and poor. The resulting shrinkage in the size of the middle class has meant fewer hand-me-downs for the poor and higher rents for the low-quality housing that is available.