In this terms Strachey lecture, Professor Monika Henzinger gives an introduction to differential privacy with an emphasis on differential private algorithms that can handle changing input data. Decisions are increasingly automated using rules that were learnt from personal data. Thus, it is important to guarantee that the privacy of the data is protected during the learning process. To formalize the notion of an algorithm that protects the privacy of its data, differential privacy was introduced. It is a rigorous mathematical definition to analyze the privacy properties of an algorithm – or the lack thereof. In this talk I will give an introduction to differential privacy with an emphasis on differential private algorithms that can handle changing input data. Monika Henzinger is a professor of Computer Science at the Institute of Science and Technology Austria (ISTA). She holds a PhD in computer science from Princeton University (New Jersey, USA), and has been the head of research at Google and a professor of computer science at EPFL and the University of Vienna. Monika Henzinger is an ACM and EATCS Fellow and a member of the Austrian Academy of Sciences and the German National Academy of Sciences Leopoldina. She has received several awards, including an honorary doctorate from TU Dortmund University, Two ERC Advanced Grant, the Leopoldina Carus Medal, and the Wittgensteinpreis, the highest science award of Austria. The Strachey Lectures are generously supported by OxFORD Asset Management