The game has changed: we write interactive web applications, we distribute the processing of huge data sets and our services need to be available at all times. This new breed of applications comes with its own set of requirements and forces us to establish new blueprints for designing our systems. In this talk we start out with the simple, classical question “for whose benefit?” and derive the four tenets of the Reactive Manifesto from this starting point. See also http://summercamp.trivento.nl/