Charles Knowlton (May 10, 1800 - February 20, 1850) was an American physician and writer. May 10 is the 130th day of the year in the Gregorian Calendar (131st in leap years). ... 1800 (MDCCC) was an common year starting on Wednesday (see link for calendar). ... February 20 is the 51st day of the year in the Gregorian Calendar. ... 1850 was a common year starting on Tuesday (see link for calendar). ...

His most famous work was a pamphlet on birth control, The Fruits of Philosophy, or the Private Companion of Young Married People (published anonymously in 1832): Knowlton was prosecuted a number of times for the publication, resulting in his being sentenced to three months hard labour in December 1832. The pamphlet reached its widest circulation in the late 1870s, as the result of the widely publicised trial of Charles Bradlaugh and Annie Besant for republishing the pamphlet in Britain. Birth control is a regimen of one or more actions, devices, or medications followed in order to deliberately prevent or reduce the likelihood of a woman giving birth or becoming pregnant. ... Charles Bradlaugh (26 September 1833 _ 30 January 1891) was a political activist and one of the most famous English atheists of the 19th century. ... Annie Besant Plaque on house in Colby Road, London SE19 where Annie Besant lived in 1874. ...

Knowlton is considered a pioneer of the Freethinkers movement.

While a medical student he was given a two month jail sentence for exhuming a corpse for the purpose of anatomical study. His medical degree was earned in 1824 from Dartmouth College.

Knowlton's opposition to Christian influence was made manifest in 1829 when he published Elements of Modern Materialism in which he referred to himself as an "infidel."

His book Fruits of Philosophy; or, the Private Companion of Young Married People was published in 1832. The book, originally published anonymously, dealt with the subject of birth control. There were eight subsequent editions of the book published in the United States. It was later republished by a group of Harvard Medical Schools doctors as a subscription in 1877.

In December 1832 Knowlton was fined at Tauton, Mass and sentenced to three months' hard labor in the House of Correction at Cambridge. Upon his release from incarceration he joined himself to a freethought society led by Abner Kneeland.

At the prompting of a minister, Knowlton was again prosecuted, this time in Greenfield, Massachusetts. Unlike the previous occasion, Knowlton was not convicted.