 The European Code of Conduct for Data Center Energy Efficiency Program was established in 2008 to help reduce the energy consumption of data centers and mitigate the associated environmental, economic, and energy supply security risks. The program has been successful in reducing the power usage effectiveness, PUE, of participating data centers, which indicates that voluntary approaches can be effective in addressing climate and energy issues. This article was authored by Maria Evgerina, Paolo Bertaldi, and Luca Castellazzi.