Levie Jacob "Louis" Fles (19 October 1872 – 24 May 1940) was a Dutch businessman, activist and author. He is best known for writing and broadcasting against Zionism, Nazism, and organized religion. A self-described freethinker, Fles was a vocal supporter of Humanism and Jewish assimilation. His relationship with the Dutch Social Democratic Workers' Party was more problematic. While he generally supported the ideals of socialism, he wrote extensively about his disagreements with the party as well. After a life filled with personal tragedy and devotion to political and social activism, Fles committed suicide in May 1940, only a few weeks after the German occupation of the Netherlands.

Louis Fles was born in Maassluis, Netherlands on 19 October 1871 to Jewish parents. His father, Jacob Levie Fles, worked as a diamond cutter, and his mother, Saartje van Blijdestein, ran a hosiery shop, placing young Louis squarely in the newly expanding merchant class. After his father died in 1873 his mother married a man named Swaab. Upon his mother's death in 1878, Louis was taken in and raised by his stepfather's family. As a successful business owner himself, Swaab took the young Louis into his company shortly after the boy had completed primary school.

On 13 August 1896 Fles married Zipporah van Straten in the city of Rotterdam. They had six children; Mina, Rosine, Henriette, Clara, Barthold, and George. Barthold became a successful literary agent in New York City in the United States. George worked as a translator in the Soviet Union during the regime of Joseph Stalin. In 1938 George was arrested as a political dissident due to his Trotskyist sympathies. Upon hearing of George's arrest, Louis travelled to Moscow, but was unable to find his son before his visa expired. George died in prison in 1939. Around this same time news arrived from the United States that daughter Rosine had died shortly after giving birth.

Fles was widely known as an opponent of Nazism when the German army occupied the Netherlands in May 1940. Even so, it was a shock to many of his family members when, on 25 May 1940, Fles committed suicide by means of pills acquired from a pharmacist in Keppel. He was buried in Amsterdam in Zorgvlied Cemetery.

Fles began working in his stepfather's office shortly after completing primary school. Soon, however, he went into business for himself. He gave lessons in French, English, and German before passing the accounting examination. This allowed him to become a bookkeeper for the Bank of Amsterdam.

With these experiences as a foundation, Fles soon founded his own company. Fles & Company had many interests, all related to serving the needs of other businesses. These included advertising and publishing, as well as the import and sale of high-end German-made Adler typewriters. The addition of a highly successful line of office furniture helped the company expand and establish branch offices throughout the Netherlands.

The rise of Nazism in Germany presented both moral and practical problems for the importer of German goods. In 1933, Fles published the brochure Hitler, hervormer of misdadiger? (Hitler, reformer or criminal?) in which he called for a boycott on the importation of all German goods. Fles sold his business and retired in 1934.

Fles' earliest published pamphlets, Is in de moderne boekhouding plaats voor het copieboek? (Can copybooks serve a function in modern accounting?) (1918) and Efficiency (1922), were both related to the world of business. However, Louis Fles is better known for his extensive writings on politics, religion, and education. As early as 1917, De Groene Amsterdammer printed his criticism of the way Social Democratic Workers' Party (SDAP) allowed churches to influence the Dutch educational system. In this article, he accused the SDAP of having "sacrificed children to politics".