Around the world the legislative requirements on battery safety are currently strengthened due to the increasing market share of battery electric vehicles. In this context, the main safety concern and the biggest challenge is avoiding thermal propagation (TP), i.e. avoiding a “cascading wildfire” within the battery system caused by a thermal runaway (TR) of a single cell. China set standards in the regulation of TP requirements a few years ago, but battery requirements are currently being revised worldwide, particularly regarding TP. This article first provides an overview of the currently applicable legislative requirements regarding thermal propagation and which updates on these requirements are expected shortly. Secondly, statistical evaluations of the “TP performance” of current battery systems is shown, based on FEV`s project experience with a large number of TP tests. The third part of this article provides an overview of influencing factors, strategies for the efficient development of optimized battery architectures and a systematic validation strategy to ensure early fulfillment of the most demanding technical challenges of battery technology relevant for homologation. Finaly the design and simulation tool chain is discussed.