We review the design challenges faced by MPSoC designers at all levels. Starting at the application level, there is a need for programming models and communications APIs that allow applications to be easily re-configured for many different possible architectures without tedious rewriting, while at the same time ensuring efficient production code. Synchronisation and control of task scheduling may be provided by RTOS's or other scheduling methods, and the choice of programming and threading models, whether symmetric or asymmetric, has a heavy influence on how best to control task or thread execution. Debugging MP systems for the typical application developer becomes a much more complex job, when compared to traditional single-processor debug, or the debug of simple MP systems that are only very loosely coupled. The interaction between the system, applications and software views, and processor configuration and extension, adds a new dimension to the problem space. Zeroing in on the optimal solution for a particular MPSoC design demands a multi-disciplinary approach. After reviewing the design challenges, we end by focusing on the requirements for design tools that may ameliorate many of these issues, and illustrate some of the possible solutions, based on experiments.