Lawrence Summers in The Atlantic:
Piketty’s timing may be impeccable, and his easily understandable but slightly exotic accent perfectly suited to today’s media; but make no mistake, his work richly deserves all the attention it is receiving. This is not to say, however, that all of its conclusions will stand up to scholarly criticism from his fellow economists in the short run or to the test of history in the long run. Nor is it to suggest that his policy recommendations are either realistic or close to complete as a menu for addressing inequality.
Start with its strengths. In many respects, Capital in the Twenty-First Century embodies the virtues that we all would like to see but find too infrequently in the work of academic economists. It is deeply grounded in painstaking empirical research. Piketty, in collaboration with others, has spent more than a decade mining huge quantities of data spanning centuries and many countries to document, absolutely conclusively, that the share of income and wealth going to those at the very top—the top 1 percent, .1 percent, and .01 percent of the population—has risen sharply over the last generation, marking a return to a pattern that prevailed before World War I. There can now be no doubt that the phenomenon of inequality is not dominantly about the inadequacy of the skills of lagging workers. Even in terms of income ratios, the gaps that have opened up between, say, the top .1 percent and the remainder of the top 10 percent are far larger than those that have opened up between the top 10 percent and average income earners. Even if none of Piketty’s theories stands up, the establishment of this fact has transformed political discourse and is a Nobel Prize-worthy contribution.