Austrian economic theory is the purest form of free market economic theory. It is comprehensive in its scope and by far the most critical of intervention into the economy by state officials.
It written for intelligent laymen as well as professional economists.
Austrian economic theory was developed by three scholars who lived in Vienna. Two of them taught at the University of Vienna: Carl Menger and Eugen von Bohm-Bawerk. The third figure, Ludwig von Mises, was a student of Bohm-Bawerk. Menger's first book, Principles of Economics, was published in 1871. Mises' final major book, Human Action, was published in 1949.
All of the following books are available free for downloading. They are in the order of difficulty, easiest to most difficult.
Gene Callahan, Economics for Real People
Ludwig von Mises, Economic Policy
Murray Rothbard, Making Economic Sense
Murray Rothbard, What Has Government Done to Our Money?
Gary North, Mises on Money
David Gordon, An Introduction to Economic Reasoning
Thomas Taylor, An Introduction to Austrian Economics
Carl Menger, Principles of Economics
Murray Rothbard, Man, Economy, and State and the Study Guide
Ludwig von Mises, Human Action