According to Brian Doherty, libertarianism is “a simple idea with rich and complicated implications: government, if it has any purpose (many libertarians think it doesn’t), should do nothing but protect its citizens’ lives and property from direct violence and theft.” Modern Libertarianism is a history of the authors, funders, and think tankers who promoted that idea in the twentieth century. It serves as a shorter historical introduction to the movement than Doherty’s longer, more comprehensive history, Radicals for Capitalism.After a brief introduction to classically liberal ideas prior to the twentieth century, Doherty quickly turns to Ludwig von Mises and F. A. Hayek, two Austrian scholars whose voluminous works in economics and political theory laid the intellectual foundations of contemporary libertarianism.Three women—Isabel Patterson, Rose Wilder Lane, and Ayn Rand—served as “founding mothers” of the movement, with Rand’s writings in particular both selling wildly and exercising a deep influence on the “Objectivist” strand of libertarianism.Other notable intellectuals include Murray Rothbard, an anarcho-capitalist who doubted government had a legitimate purpose, and Milton Friedman, the Nobel Prize-winning economist whose Capitalism and Freedom and Free to Choose made a robust intellectual case for “how, where, and why government fails and why private markets are both morally and practically better,” as Doherty puts it.Other prominent intellectuals Doherty briefly profiles include the philosopher Robert Nozick, constitutional scholar Randy E, Barnett, and economists Israel Kirzner, and James M. Buchanan.Much less known is the Volker Fund, a foundation that supported libertarian proponents in the early and mid-twentieth century, long before their ideas became more mainstream. A number of think tanks also arose over the years to promote classical liberal ideas, including the Foundation for Economic Education, the Institute for Humane Studies, and especially the Cato Institute.Libertarian ideas influenced Republican presidential candidates Barry Goldwater in 1964 and Ronald Reagan in 1980. Goldwater lost his race, and Reagan went on to disappoint libertarians with many of his policy decisions. Doherty profiles the Libertarian Party, the largest and most successful of twentieth-century third parties, whose impact nonetheless seems negligible despite its relative size.The final chapter rushes through the nearly forty years since Reagan’s administration. Despite the mainstreaming of libertarian ideas, some of which are quite popular, government has steadily grown in size and reach, to the point where the national debt—as just one indication—now constitutes 120% of annual GDP, For the purpose of comparison, in 1946, after five years of world war, the national debt peaked at 106%. A peacetime budget with wartime levels of debt is unsustainable and threatens the financial wellbeing of every citizen.The growth of government guarantees that libertarian ideas will continue to receive a hearing, but it’s an open question whether they will be actually heard.I recommend Modern Libertarianism as a short history of the movement, though I cannot endorse every person or idea it describes, and Doherty doesn’t either. (Honestly, some of the figures strike me as weird.) I am sympathetic to libertarianism, though I wouldn’t describe myself as a libertarian.Regardless, libertarianism’s defense of individual liberty, the effectiveness of market solutions, and the hazards and unintended consequences of state action serves as a useful counterweight to calls on both Left and Right for government at all levels to do more.Sometimes, libertarians would remind us, less (or nothing at all) is more.