The General Theory of Employment, Interest and Money (Timeless Wisdom Collection Book 951)

This book has generally considered Keynes greatest work, and is largely credited with creating the terminology and shape of modern macroeconomics. Published in 1936, it sought to bring about a revolution, the "Keynesian Revolution", in the way economists thought – especially in relation to the proposition that a market economy tends naturally to restore itself to full employment after temporary shocks. Cornerstone of the Keynesian thought, this book challenged the established classical economics and introduced important concepts such as the consumption function, the multiplier, the marginal efficiency of capital, the principle of effective demand and liquidity preference.
A must read to anybody interested in economics, as it contains timeless truths.