John M. Barry (born April 12, 1947)[1] is an American author and historian who has written books on the Great Mississippi Flood of 1927, the influenza pandemic of 1918, and the development of the modern form of the ideas of separation of church and state and individual liberty.

Roger Williams and the Creation of the American Soul: Church, State, and the Birth of Liberty (2012) Two of his books involved him directly in policy-making.

He has advised the private sector and local, state, national, and international government officials about preparing for another influenza pandemic.

Recognizing that protecting New Orleans from storm surge required restoring much of coastal Louisiana, which had once served as a buffer between the city and the ocean and 2,000 square miles of which had disappeared, he proposed to the levee board that it file a lawsuit against oils companies responsible for a significant amount of the damage.

His colleagues agreed and on July 24, 2013, SLFPAE filed a lawsuit against Exxon Mobil, BP, Shell, Chevron and 94 other oil, gas, and pipeline companies for their role in damage to Louisiana's coast.

In August 2014, attorneys for the board filed a motion seeking a partial summary judgment arguing that Act 544 does not apply to the flood authority and that the law is unconstitutional.

[4] Barry has written for The New York Times, The Wall Street Journal, Time Magazine, Fortune, The Washington Post, Esquire, and other publications and frequently appears as a guest commentator on networks in the U.S., including on NBC's Meet the Press, ABC's World News Tonight, PBS's The News Hour, numerous NPR shows, and such foreign media as the BBC and Al Jazeera.