Using natural gas as a fuel in combustion engines is a promising way to obtain efficient power generation with relatively low environmental impact. Dual fuel operation is especially interesting, because it combines the safety and reliability of the basic diesel concept with great flexibility in the choice of fuel. Due to the increased number of degrees of freedom of dual fuel combustion concepts it is imperative to use simulation methods in the development process. This paper presents the current engineering and research efforts with focus on the 3D CFD simulation of ignition and combustion of a premixed natural gas/air charge with a diesel pilot spray. The highly transient behavior of the diesel injector especially at small injection quantities poses challenges to the numerical simulation of the spray. Design of Experiments (DoE) methods were applied to identify adequate parameter sets for the spray models. To depict dual fuel combustion, a widely used approach, the Extended Coherent Flame Model with the 3 zone approach (ECFM-3Z) is applied. With this approach, it is possible to calculate all three combustion regimes simultaneously. Several adjustments are necessary to depict the dual fuel combustion processes accurately, namely the treatment of the ignition delay for the dual fuel mixture, the initial flame surface density deposition and the flame front propagation throughout the lean gas-air mixture. Detailed chemistry calculations using a dedicated dual fuel mechanism have been performed for the ignition delay tabulation, which has been extended to cover the two different fuels used in this combustion mode. A formulation for the initial flame surface density that includes thermal expansion of the gas and turbulence influences has been found. The flame front propagation is then also influenced by the laminar flame speed, a parameter that depends on the fuels. Finally, the developed models are thoroughly validated by measurement data from a single cylinder research engine.