ASCEND is a free, open source, mathematical modelling system developed at Carnegie Mellon University since the late 1980s. Its main uses have been in the field of chemical process modelling although its capabilities are general. It includes nonlinear algebraic solvers, differential/algebraic equation solvers, nonlinear optimisation and modelling of multi-region 'conditional models'. Its matrix operations are supported by an efficient sparse matrix solver called mtx.

Ascend means to go up, fly, or soar.