The data center sector is the fastest growing consumer of electricity. How do we make this vital part of the economy sustainable? In Stockholm, we believe the way forward is to think of the city as a circular flow of resources. Stockholm targets to be fossil fuel free by 2040, and as part of realizing that aim we want to recycle the waste heat of data centers. In this presentation, Erik Rylander presents how Stockholm Data Parks and Stockholm Exergi have succeeded in establishing a city-wide system where the excess heat of data centers is reused to heat the citizens of Stockholm. Erik also discusses what the key success factors are for making heat recovery work on a large scale. In concluding his presentation, Erik points to other challenges the city is facing in the transformation to a sustainable future, and how Stockholm Exergi is aiming provide solutions allowing all Stockholmers to become sustainable.