Paul Cassirer (21 February 1871, in Görlitz – 7 January 1926, in Berlin) was a German art dealer and editor who played a significant role in the promotion of the work of artists of the Berlin Secession and of French Impressionists and Post-Impressionists, in particular that of Vincent van Gogh and Paul Cézanne.

Paul Cassirer started out as a student of art history, and then became a writer in 1890s Munich, where he worked for the weekly magazine Simplicissimus and published two novels.

Cassirer moved to Berlin, and he and his cousin Bruno, while still in their mid 20s, opened their gallery on the ground floor of Paul's house in the up-market Viktoriastrasse. The cousins came from a prominent family, whose members included the neurologist Richard Cassirer and the philosopher Ernst Cassirer. Paul was born into a Jewish family. His father, Louis, was an engineer and businessman, whose company — Kabelwerke Dr. Cassirer & Co. — manufactured telegraphic cables, and was eventually taken over by Siemens.

In 1895 he married Lucie Oberwarth.

In 1901 Cassirer visited Julien Leclercq's retrospective of Van Gogh's work, and later that year he organized the inclusion of five Van Gogh canvases in the May show of the Berlin Secession.

On 21 May 1904, Cassirer and Lucie divorced.

In 1910 he married Ottilie Godefroy (18 August 1880, Vienna – 21 February 1971, Berlin), the actress well known under her pseudonym Tilla Durieux. Tilla had very briefly been married to the painter Eugen Spiro six years earlier. She and Cassirer were married for sixteen years, but the union was to end tragically.

In 1910 Cassirer also resurrected the periodical Pan.