OpenStudio is a cross-platform (Windows, Mac, and Linux) collection of software tools to support whole building energy modeling using EnergyPlus and advanced daylight analysis using Radiance. OpenStudio is an open source project to facilitate community development, extension, and private sector adoption. OpenStudio includes graphical interfaces along with a Software Development Kit (SDK). The graphical applications include the Trimble SketchUp Plug-in, RunManager, and ResultsViewer. The Trimble SketchUp Plug-in is an extension to Trimble’s popular 3D modeling tool that adds EnergyPlus context to the SketchUp program. The Plug-in allows users to quickly create geometry needed for EnergyPlus using the built-in functionality of Trimble SketchUp including existing drawing tools, integration with Google Earth, Building Maker, and Photo Match. RunManager manages simulations and workflows and gives users access to the output files through a graphical interface. ResultsViewer enables browsing, plotting, and comparing EnergyPlus output data, especially time series.