Je sais tout was a French magazine established by Pierre Lafitte in 1905. It was noted for its publication of the works of Maurice Leblanc, in particular the adventures of Arsène Lupin. It appeared on the 15th of each month, but publication was interrupted from August 1914 to the end of 1914. The magazine's format was usually 17.5cm by 24.5cm, and contained more than 100 pages. The magazine's logo was created by Jules Alexandre Grün. Initial circulation figures were estimated to be about 250,000.