Fifty-nine (59, LIX) is the natural number following fifty-eight and preceding sixty.

Fifty-nine is the 17th smallest prime number. The next is sixty-one, with which it comprises a twin prime.

Fifty-nine is also:

• The atomic number of praseodymium, a lanthanide.
• The number of icosahedra discussed in H. S. M. Coxeter, P. Du Val, H. T. Flather, and J. F. Petrie's book The Fifty-Nine Icosahedra.
• The designation of Interstate 59, a freeway that runs from Louisiana to Georgia.