MINOTAUR is a toolkit for solving mixed-integer nonlinear optimization problems, where some of the variables are restricted to take integer values. MINOTAUR implements a range of standard techniques, such as branch-and-bound and branch-and-cut, and is written to be extensible to accommodate new algorithmic paradigms as well as new problem classes. The MINOTAUR library can also be used to customize algorithms to exploit on specific problem structures.