In the online world, user engagement refers to the quality of the user experience that emphasizes the positive aspects of the interaction with a web application and, in particular, the phenomena associated with wanting to use that application longer and frequently. User engagement is a key concept in the design of web applications, motivated by the observation that successful applications are not just used, but are engaged with. Users invest time, attention, and emotion in their use of technology, and it must satisfy both their pragmatic and hedonic needs and expectations. Measurement is key for evaluating the success of information technologies, and is particularly critical to any web applications, from media to e-commerce sites, as it informs our understanding of user needs and expectations, system design and functionality. For instance, news portals have become a very popular destination for web users who read news online. As there is great potential for online news consumption but also serious competition among news portals, online news providers strive to develop effective and efficient strategies to engage users longer in their sites. Measuring how users engage with a news portal can inform the portal if there are areas that need to be enhanced, if current optimization techniques are still effective, if the published material triggers user behavior that causes engagement with the portal, etc. Understanding the above is dependent upon the ability to measure user engagement. The focus of this tutorial is how user engagement is currently being measured and future considerations for its measurement. This tutorial is part of the World-Wide-Web Conference, held in Rio to Janeiro, May 2013.