The energy transition is driving extensive changes to global energy systems, including the electrification of heating and mobility, increased renewable electricity generation, and a shift towards sustainable gases like green hydrogen. These changes will need to be accompanied by major investments in energy infrastructure, especially considering the goals of climate-neutrality envisioned for 2050. In integrated energy system planning, the system-level interactions between, for example, storage, electricity networks and gas networks are taken into account and considered as a whole. This thesis investigates the potential benefits of integrated energy system planning, focusing on the distribution grid level. The analysis is carried out for a case study in the Sterrenburg region of South Holland. Power-gas integration and the integration of electrical energy storage with batteries are investigated using hourly demand and generation profiles based on 2050 scenarios. An expansion planning model is developed to determine the optimal investments for the 2050 scenarios, starting from the existing network. This mixed-integer linear programming model uses PyPSA, an open-source energy system modelling toolbox. The optimisation objective is a combination of investment and operational costs. The results demonstrate spatial and economic benefits from including electrolysis, and limited effects from electric storage and gas-to-power within the scope of the case. There are many possibilities for broadening and deepening the scope in future works. For example, different combinations of integration such as heat networks and long-term gas storage could be considered together.