Isabel Paterson (January 22, 1886 – January 10, 1961) was a Canadian-American libertarian writer and literary critic. Historian Jim Powell has called Paterson one of the three founding mothers of American libertarianism, along with Rose Wilder Lane and Ayn Rand, who both acknowledged an intellectual debt to Paterson. Paterson's best-known work, The God of the Machine (1943), a treatise on political philosophy, economics, and history, reached conclusions and espoused beliefs that many libertarians credit as a foundation of their philosophy. Her biographer Stephen D. Cox (2004) believes Paterson was the "earliest progenitor of libertarianism as we know it today." In a letter of 1943, Rand wrote that "The God of the Machine is a document that could literally save the world ... The God of the Machine does for capitalism what Das Kapital does for the Reds and what the Bible did for Christianity."

Born Isabel Mary Bowler in rural Manitoulin Island, Ontario, she moved with her family to the west when she was very young. She grew up on a cattle ranch in Alberta. Paterson's family was quite poor and she had eight siblings. A voracious reader who was largely self-educated, she had brief and informal public schooling during these years: about three years in a country school, from the ages of 11 to 14. In her late teen years, Bowler left the ranch for the city of Calgary, where she took a clerical job with the Canadian Pacific Railway. As a teenager, she worked as a waitress, stenographer, and bookkeeper, working at one point as an assistant to future Canadian Prime Minister R. B. Bennett.

This hardscrabble youth probably led Paterson to attach great importance to productive "self-starters". Although she was articulate, well-read, and erudite, Paterson had extremely limited formal education, an experience she shared with Rose Wilder Lane, who was also Paterson's friend and correspondent for many years.

In 1910, at the age of 24, Bowler entered into a short-lived marriage with Canadian Kenneth B. Paterson. The marriage was not happy, and they parted in 1918. It was during these years, in a foray south of the border, that Paterson landed a job with a newspaper, the Inland Herald in Spokane, Washington. Initially she worked in the business department of the paper, but later transferred to the editorial department. There her journalistic career began. Her next position was with a newspaper in Vancouver, British Columbia, where for two years she wrote drama reviews.

In 1914, Paterson started submitting her first two novels, The Magpie's Nest and The Shadow Riders, to publishers, without much success. It was not until 1916 that her second novel The Shadow Riders was accepted and published by John Lane Company, which also published The Magpie's Nest the following year in 1917.

After World War I, she moved to New York City, where she worked for the sculptor Gutzon Borglum. He was creating statues for the Cathedral of St. John the Divine and would later carve the memorial at Mount Rushmore. Paterson also wrote for the World and the American in New York.

In 1921, Paterson became an assistant to Burton Rascoe, the new literary editor of the New York Tribune, later the New York Herald Tribune. For 25 years, from 1924 to 1949, she wrote a column (signed "I.M.P.") for the Herald Tribune's "Books" section. Paterson became one of the most influential literary critics of her time. She covered a time of great expansion in the United States literary world, with new work by the rising generation of Ernest Hemingway, F. Scott Fitzgerald and many others, African Americans of the Harlem Renaissance, as well as the first American generation of the great waves of European immigrants. Her friends during this period included the famous humorist Will Cuppy. In 1928 she became an American citizen, at the age of 42.

She was notorious for demonstrating her sharp wit and goring of sacred cows in her column, where she also first articulated many of the political ideas that reached their final form in The God of the Machine. Her thinking, especially on free trade, was also foreshadowed in her historical novels of the 1920s and 1930s. Paterson opposed most of the economic program known as the New Deal, which American president Franklin D. Roosevelt put into effect during the Great Depression. She advocated less government involvement in both social and fiscal issues.