Information and communication technology plays an important role in addressing the world’s energy problem. Networked digital electricity meters (so-called smart meters), for instance, can provide households with real-time information on their electricity consumption and thus help them to conserve energy. Initial expectations on the saving potential of this technology were too optimistic, however. In fact, recent pilot studies conducted under realistic assumptions have shown that savings induced by plain electricity consumption feedback are often significantly lower than many have originally expected. In this dissertation, we take smart metering to a new level as we explore a data analysis-driven approach to personalize energy efficiency services that may be offered at large scale. An example for such a service is automated energy consulting, which consists in automatically providing energy saving recommendations to households by taking into account their appliance stock and usage profiles. In addition, we provide the foundation for an electricity bill that is tailored to the household as it shows the contribution of individual appliances to the overall bill or compares a household’s consumption with other households that have similar characteristics. Behavioral trials indicate that such consumption feedback is potentially more successful in motivating households to reduce their electricity consumption than plain consumption feedback or generic energy saving recommendations. One contribution of this thesis is the design, development, and evaluation of a system that automatically estimates characteristics of a household (like its socio-economic status, dwelling properties, and appliance stock) from the household’s electricity consumption data. We evaluate our approach on real world smart meter data collected from more than 4000 households over a period of 1.5 years. Our analysis shows that inferring household characteristics is feasible, as our method achieves an accuracy of more than 70% over all households for many of the characteristics and even exceeds 80% for some of the characteristics. For utilities, the system creates valuable customer insights that - without having to perform costly and cumbersome surveys - help to run energy efficiency campaigns more efficiently by targeting each household with the adequate service (e.g., offering energy consulting for retired people and a smart heating system, which automatically controls the thermostat based on occupancy, for employed people). Furthermore, these insights can be used to realize automated peer group comparisons on the electricity bill or in an online portal. Providing automated, household-specific energy saving recommendations requires more detailed information about a household than its high-level characteristics. In particular, it is important to know when individual appliances are running and how much they consume. To avoid measuring each appliance individually through a complex sensing infrastructure, we investigate inferring this information from the overall electricity consumption measured by a smart meter. To explore this concept (non-intrusive load monitoring, NILM), we developed an evaluation framework and analyzed the performance of several state-of- the-art NILM algorithms. To this end, we collected electricity consumption data in six Swiss households over a period of eight months and made it publicly available. Along with fine-grained smart meter data (collected at 1 Hz), our data set contains ground truth measurements of 47 selected appliances and each of the household’s occupancy state. Our analysis shows that - through the enhancement of an existing NILM algorithm - it is possible to achieve recognition rates of more than 90% for some typical appliances. This is sufficient for energy consulting scenarios; its practical use is limited, however, since a training period is required. Ultimately, deploying smart meters comes with a cost that - for some of the households - can be higher than the achievable savings given today’s energy prices. Maximizing societal benefits thus requires a well-managed interplay between (1) regulators, which define rules for smart meter deployments and set penalties if saving targets are not reached, (2) utilities, which develop and run energy efficiency campaigns, and (3) households, which should invest in energy saving solutions or adapt their lifestyle in order to use energy more efficiently. This thesis copes with this challenge as it shows how to utilize Internet of Things technologies and machine learning methods to enable personalized energy efficiency services that scale to thousands or even millions of households. We develop methods, build open source evaluation frameworks, and collect and analyze real world consumption data in order to better understand residential electricity consumption and improve the effect (and thus the value) of smart meter deployments and feedback mechanisms.