Heading towards exascale, the challenges for process management with respect to flexibility and efficiency grow accordingly. Running more than one application simultaneously on a node can be the solution for better resource utilization. However, this approach of co-scheduling can also be the way to go for gaining a degree of flexibility with respect to process management that can enable some kind of interactivity even in the domain of high-performance computing. This chapter gives an introduction into such co-scheduling policies for running multiple MPI sessions concurrently and interactively within a single user allocation. The chapter initially introduces a taxonomy for classifying the different characteristics of such a flexible process management, and discusses actual manifestations thereof during the course of the reading. In doing so, real world examples are motivated and presented by means of ParaStation MPI, a high-performance MPI library supplemented by a complete framework comprising a scalable and dynamic process manager. In particular, four scheduling policies, implemented in ParaStation MPI, are detailed and evaluated by applying a benchmarking tool that has especially been developed for measuring interactivity and dynamicity metrics of job schedulers and process managers for high-performance computing.