Data streams relevant for energy use in buildings are increasing. Many households have “smart” meters in place or are installing smart thermostats or smart plugs; and the first IoT applications are entering households. We see similar developments in commercial buildings. This wealth of data provides new opportunities to better understand and control energy use in buildings. Significant energy saving potentials are claimed. Nevertheless, there are also serious challenges, like privacy and cybersecurity issues, and the variety of platforms. In this webinar an overview will be given of the main developments in this new field. The challenge is how big data can empower users of homes and office buildings to create a comfortable and efficient living and working place.