This essay relates recent developments in growth theory to problems and ideas that first engaged R. F. Harrod, E. Domar, and their neoclassical successors. The body of 'new growth theory' began by finding special ways to assume that there are constant returns to capital. It is shown that this is...

International productivity comparisons can be built up with micro and macro data. Studies of firms or groups of firms producing similar outputs reveal the deeper causes of differences in productivity across countries. The studies find that such differences often depend on patterns of...

My main goal in this essay is to say something about leftover open questions in macroeconomics, as well as new phenomena that need to be accommodated in early 21st century macroeconomics, and the sorts of ideas that might make progress possible. The essay first considers foundational questions...