**The Mathematical Diary** was an early American mathematical journal and mathematics magazine, published between 1825 and 1833.

The *Mathematical Diary* was founded by Robert Adrain at Columbia College (now Columbia University) after two unsuccessful attempts, in 1808 and 1814, to start a more purely academic mathematics journal, *The Analyst, or, Mathematical Museum*. The *Mathematical Diary* contained, in addition to some serious mathematics, articles of general interest such as mathematical puzzles aimed at the amateur problem-solver, which may have helped it attract more laypeople as subscribers and contributed to its greater longevity. Adrain edited the first four issues; after he left Columbia in 1826 for Rutgers, James Ryan, previously the publisher, took over the editorship. A total of thirteen issues were published.