Recent advances in quantum technology - from quantum computers and simulators to secure communication and metrology - have not only opened up a whole new world of practical applications but also changed our understanding of quantum theory itself. This text introduces quantum theory entirely from this new perspective. It does away with the traditional approach to quantum theory as a theory of microscopic matter, and instead focuses on quantum theory as a framework for information processing. Accordingly, the emphasis is on concepts like measurement, probability, statistical correlations, and transformations, rather than on waves and particles. This affords a simple, direct route to quantum theory, all the way to some of its most fascinating conceptual issues.