Validation of software releases for CMS

The CMS software stack currently consists of more than 2 Million lines of code developed by over 250 authors with a new version being released every week. CMS has setup a release validation process for quality assurance which enables the developers to compare to previous releases and references. This process provides the developers with reconstructed datasets of real data and MC samples. The samples span the whole range of detector effects and important physics signatures to benchmark the performance of the software. They are used to investigate interdependency effects of software packages and to find and fix bugs. The samples have to be available in a very short time after a release is published to fit into the streamlined CMS development cycle. The standard CMS processing infrastructure and dedicated resources at CERN and FNAL are used to achieve a very short turnaround of 24 hours. The here described release validation process is an integral part of CMS software development and contributes significantly to ensure stable production and analysis. It's success emphasizes the importance of a streamlined release validation process for projects with a large code basis and significant number of developers and can function as an example for future projects.