Over the last decade, significant progress has been achieved in the commercialization of Polymer Electrolyte Membrane (PEM) fuel cells for mobile applications. However, long-term durability and stability of such systems still needs further improvement. To overcome today’s time-consuming long-term durability tests, the development of so-called accelerated durability tests (ADT) is urgently necessary. In this work, we present our recent results on such ADT test-protocols based on research promoting a detailed understanding of the individual aging mechanisms in PEM fuel cells.Various stressors had been investigated separately to understand their impact on overall fuel cell ageing. Certain levels of cell potential, temperature and humidity could be identified as major stressors and were successively added to the test protocol. In addition to the electrochemical test results, additional focus was put on different in-situ and ex-situ characterization methods. This combination enables a detailed understanding of individual stressors and their interply. The PEM-stack used in this study is an automotive high-performance stack developed within the publically funded Auto Stack Industry (ASI) project. An extensive long-term test over 5,500 operating hours was carried out as baseline test using the New European Driving Cycle, but with additional features to mimic realistic automotive load-profiles. Based on the results of this reference protocol, four different ADT protocols of only 1,200 hours test duration were derived. All tests were performed using short stacks with automotive-size active area. In-situ measurements include spatially resolved current measurement, cyclic voltammetry and impedance spectroscopy. After each test, selected cells were additionally analyzed ex-situ using layer thickness measurement via SEM, IR-thermography and contact angle measurements.The results from ex-situ investigations underline the degradation models postulated from in-site measurements. The overall data show that detailed understanding of individual stressors is necessary to successfully develop reliable accelerated ageing tests for PEM fuel cells.