To achieve net-zero emissions by the middle of the century, fossil fuels must be replaced as the main source of energy with more sustainable alternatives such as wind or solar power. To do so, high levels of interoperability, or the ability for technologies to seamlessly integrate, effectively communicate, and undertake tasks to achieve desired outcomes, are required. However, there is no universal approach, and interoperability in the energy system must be determined in specific use cases. This Toolkit note discusses why interoperability is necessary in the energy system, the benefits and challenges to realising interoperability in the energy sector, and the role of policy in fostering interoperability to achieve net-zero emissions in the medium-term. The note argues for greater use of open data to maximise electricity system efficiency, an increase in the use of low-carbon energy, and the minimisation of the long-term costs of increased electricity demand.