This document provides guidance on how to use an open source software (OSS) approach to support technology transition. Using an OSS approach can enable and speed technology transition, but many researchers and government program managers are unfamiliar with how to use it. The goal of this guide is to help researchers (including principal investigators) turn their ideas into successfully deployed solutions, and also to help program managers as they select research proposals and oversee researchers’ work. It discusses how to build on existing work (including how to evaluate existing software and modify existing OSS), establish a collaborative environment for a new OSS project when necessary, the key issues in OSS project inputs and results, tips for making an OSS project successful, and approaches for overcoming common impediments.