Abstract: Our research goal is to provide a better understanding of user engagement and how to measure it. Our view is that we should not speak of one main approach to measure engagement - e.g.through one or a fixed set of metrics -- because engagement depends on the online services at hand. Instead, we should be talking of models of user engagement. By analysing a number of services offered by a large internet company, we show that it is possible to derive effectively simple models of user engagement. This paper provides a first taxonomy of user engagement patterns, allowing for a better understanding of the important characteristics of user engagement of a service or group of services.