Privacy by design requires integrating data protection into systems from the outset, during their design, rather than building it in later. Related legislation does not specify how to achieve this and mainstream languages and frameworks lack support for privacy by design. To address this long-standing problem, we have developed different, effective technical solutions. First, we have developed powerful logic-based tools that enforce formal data protection policies at runtime by controlling relevant system actions. Second, we have proposed methods and tools for integrating privacy models into system design models, enabling model-driven privacy enforcement. We report on our methods, tools, and practical experiences using them.