Electrifying the world is one of the pragmatic solutions for reducing carbon footprint. Electric transportation, renewable energy generation, electric storage, smart and micro grid technologies, as well as digitalization are essential parts of sustainable electricity systems. These technologies are supported by power electronics as the core of their energy conversion process. The overall performance of modern energy systems relies on the reliable operation of power electronics which needs accurate and optimized design, planning and control of power converters. This tutorial is divided into two parts: The part “Reliability in Power Electronics Converters” introduces fundamentals of reliability terminology and failure mechanisms. Statistical aspects of reliability will be introduced, both theoretical and with a practical example. The “mission profile” incorporates the combination of loads and their duration to which the electronic system will be subjected. They determine depending on the construction (design) the physical processes and thus the life-time of the system. Most common test standards will be introduced and procedures on how to plan reliability tests are shown. Further on, typical failure mechanisms which can occur within power electronic converters are discussed. This ranges from the power devices itself to assembly aspects like chip interconnects and material fatigue in potting materials, PCBs and adhesives. As an outlook and preparation for part two, basic concepts of risk assessment techniques are presented, which can be applied on process and technology as well as converter and system level. This tutorial covers comprehensive concepts of reliability modelling, analysis and enhancement in power electronic converters. Therefore, it would be fruitful for graduate students and senior researchers both from industry and academia who are interested in converter design, reliability modelling and enhancement in Power electronics systems.