When simulation models shall be used to support decision-making, the trustworthiness of the results need to be ensured. Usually, models are validated against real-world data. Yet, in the ongoing pandemic, there is a lack of respective data that can be used to validate the model’s behaviour. To overcome this issue, this chapter discusses the validation of simulation models for the Covid-19 pandemic by comparing their results among each other. To this end, we present a formal comparison between the existing behaviour-based epidemiological model that was developed at the University of Oxford and the ASSOCC model.