The NEOS Server (Network-Enabled Optimization System) is a free internet-based service for solving numerical optimization problems. Hosted by the University of Wisconsin in Madison, the NEOS Server provides access to more than 60 state-of-the-art solvers in more than a dozen optimization categories. The NEOS Server offers a variety of interfaces for accessing the solvers, and jobs run on distributed high-performance machines. The NEOS Server is available free of charge for everyone, anywhere in the world.