Future emission legislation will be increasingly stringent. The current German TA Luft limit for nitric oxide (NOx) emissions from large gas engines is 500 mg/mn3 @ 5% O2 and there is a clear trend toward further reductions. One possible strategy to meet these limits for gas engines is exhaust gas recirculation (EGR). This paper focuses on the application of 1D simulation to a variety of different tasks in gas engine development. First, the basic effects of EGR in gas engines are explained by discussing several 1D simulation results from two 1D simulation models for a large stationary gas engine. A detailed single cylinder engine model is used to study the interaction between the pre-chamber and the main combustion chamber. The boundary conditions are provided by a multicylinder engine model that includes a turbocharger. Based on simulation calculations with both models as well as measurements from a single cylinder research engine, the thermodynamic conditions in the combustion chamber and the gas dynamics are analyzed.