GNU MPC is a C library for the arithmetic of complex numbers with arbitrarily high precision and correct rounding of the result. It extends the principles of the IEEE-754 standard for fixed precision real floating point numbers to complex numbers, providing well-defined semantics for every operation. At the same time, speed of operation at high precision is a major design goal. The library is built upon and follows the same principles as GNU MPFR. It is distributed under the GNU Lesser General Public License, either version 3 of the licence, or (at your option) any later version.