This talk was recorded at Scala Days New York, 2016. Follow along on Twitter @scaladays and on the website for more information http://scaladays.org/. Abstract: Reactive Applications are the next major evolution of the Internet. They allow for applications to be responsive, scalable and resilient by building on a fully event-driven foundation. Lightbend’s Reactive Platform, consisting of the Play Framework, the Akka middleware and the Scala programming language embraces this new programming paradigm which allows developers to write interactive applications that are always available and which adapt to changing load by being distributed by design. While the reactive approach enable us to build highly scalable and resilient applications it also introduces new challenges in how to monitor them. Almost every current monitoring tool relies on a stack frame based approach where using the stack trace can provide good answers to what caused the exceptional state. In message driven, or asynchronous, applications this approach no longer provides any good information. We therefore need to invent new approaches for how to monitor these types of applications. During this session we will cover the traditional monitoring approach, different possible ways of how to monitor asynchronous applications and finally show the way we have chosen to build a monitoring tool for reactive applications at Lightbend.