This tutorial provides an overview of VR application development using Open Source software tools. We focus on the VR Juggler suite of tools (see http://www.vrjuggler.org) and various Open Source projects that can work with it. We will demonstrate how Open Source software ensures extensibility and eases integration between software tools. We will also show how leveraging existing and emerging Open Source projects can lower development times and costs while simultaneously increasing portability and stability. In particular, we will discuss several kinds of Open Source VR software: • Development frameworks for immersive VR applications (VR Juggler) • Scene graphs for managing application data. (OpenSG or OpenSceneGraph). • Clustering software for powering low-cost VR systems (NetJuggler). • Collaboration software for writing interactive, networked applications (primarily discussing software currently under development by the VR Juggler team). • Various other tools needed to write compelling applications, such as audio libraries, scripting capabilities, and navigation systems, and how they can be used by VR Jugglerbased applications.