Industrial Control Systems (ICS) are used through- out critical national infrastructure. This has the potential to attract malicious attackers with a variety of motivations e.g. political, financial, reputational. There has been development and publication of highly technical security research, but also basic scripted attacks, which can be executed with the most limited of resources. This paper focuses on the development (design and construction) of an ICS testbed, with the view to further research in two key areas, namely security and resilience. Included is a survey detailing the approaches taken by other institutes/organisations when designing ICS testbeds. From this the key design requirements of flexibility, reliability, and credibility are drawn. A design of our testbed is provided, alongside details of future work, not only within our testbed, but also the wider context of ICS security.