In many computing applications the system needs to make decisions to serve requests that arrive in an online fashion. Consider, for instance, the example of a navigation app that responds to driver requests. In such settings there is inherent uncertainty about important aspects of the problem. For example, the preferences of the driver with respect to features of the route are often unknown and the delays of road segments can be uncertain. The field of online machine learning studies such settings and provides various techniques for decision-making problems under uncertainty.