The market economy is the social system of the division of labor under private ownership of the means of production. Everybody acts on his own behalf; but everybody’s actions aim at the satisfaction of other people's needs as well as at the satisfaction of his own. Everybody in acting serves his fellow citizens. Everybody, on the other hand, is served by his fellow citizens. Everybody is both a means and an end in himself; an ultimate end for himself and a means to other people in their endeavors to attain their own needs.
— Ludwig von Mises, Human Action 
(Hat-tip Future Freedom Foundation)