The commercial library Optimization 2.1 for interactive multi-criteria optimization tasks has been released along with Dymola 2013. The library offers several numerical optimization algorithms for solving different kinds of optimization tasks. User defined Modelica functions or models provide the basis for an interactive optimization process where the user keeps overview of complex multi-criteria optimization tasks that can take discrete parameters, several model operating points or trajectories into account. Computational performance of optimization runs can be significantly increased by parallel numerical integrations of the Modelica model on multi-core machines.