[mdcox]

For any other casual viewers unfamiliar with but interested in economics, the 'r' refers to return on capital and 'g' refers to the growth rate of the economy. This section of the wikipedia article on his book seems to give a quick and decent high level overview that puts this (and a few other comments) into perspective: https://en.wikipedia.org/wiki/Capital_in_the_Twenty-First_Ce...

[viraptor]

The whole book is great. It may be ~700 pages, but it's more of a story than a heavy economy book. If anyone is interested enough to comment on this issue, this book is definitely something you'd be interested to read.