Thomas Piketty's book, Capital in the Twenty-First Century, reopens fundamental questions about the role and rewards of capital that economists have never resolved. It does so by exploring the history of capital and derives much of its credibility from the evidence it marshals in defence of its claims. In this paper, I evaluate the basis for Piketty's arguments by considering them in light of the history of US capitalism. I argue that it is extremely difficult to make economic sense of Piketty's historical analysis of capital in the US in the 19th and 20th centuries. That is true, only in part, due to the distinctive choices he makes, compared to mainstream economists, in defining and measuring capital. Much more problematic, in fact, are theoretical commitments he shares with them that preclude an understanding of capital's historical role and rewards in the US economy. Based on a discussion of several important features of US economic history, I have argued that such an understanding demands an historical analysis of capital, both productive and financial capital, in relation to the evolving social organisation of capitalism in the US.