This book covers the results of the Teraflop Workbench, other projects related to High Performance Computing, and the usage of HPC installations at HLRS. The TeraflopWorkbench project is a collaboration between the High Performance Computing Center Stuttgart (HLRS) and NEC Deutschland GmbH (NEC-HPCE) to support users in achieving their research goals using High Performance Computing. The first stage of the Teraflop Workbench project (2004–2008) concentrated on user’s applications and their optimization for the former flag ship of HLRS, a 72- node NEC SX-8 installation. During this stage, numerous individual codes, developed and maintained by researchers or commercial organizations, have been analyzedand optimized.Within the project, several of the codes have shown the ability to outreach the TFlop/s threshold of sustained performance. This created the possibility for new science and a deeper understanding of the underlying physics.