This chapter presents a methodological framework for whole energy systems evaluation with underpinning principles, demonstrated through a case study. The framework provides a socio-technical approach for evaluation by combining stakeholders’ requirements with the system components and functions through a system-of-systems architecture methodology. The framework application involves three stages: scenario formulation, conceptual modelling and quantitative modelling, in an iterative process of feedback between the stages. The proposed framework is applied on a case study to evaluate the effectiveness of energy systems integration as a pathway for achieving the energy transition objectives. The case study is based on the local energy system of the North of Tyne region, UK. The case study demonstrates the framework application and presents evidence on the potential of energy systems integration in the region via vector-coupling technologies, including combined heat and power, power-to-gas and heat pumps, under different scenarios.