How do wealth- and capital-output ratios evolve in the long run, and why? Until recently it was difficult to properly address this question, for one … - Thomas Piketty

Capital is defined as the sum total of nonhuman assets that can be owned and exchanged on some market.

I am trying to put the distributional question and the study of long-run trends back at the heart of economic analysis. In that sense, I am pursuing a tradition which was pioneered by the economists of the 19th century, including David Ricardo and Karl Marx. One key difference is that I have a lot more historical data. With the help of , , Facundo Alvaredo, Gilles Postel-Vinay, Jean-Laurent Rosenthal, Gabriel Zucman and many other scholars, we have been able to collect a unique set of data covering three centuries and over 20 countries. This is by far the most extensive database available in regard to the historical evolution of income and wealth. This book proposes an interpretative synthesis based upon this collective data collection project.

I can now present the first fundamental law of capitalism, which links the capital stock to the flow of income from capital. The capital/income ratio β is related in a simple way to the share of income from capital in national income, denoted α. The formula is