This document provides an overview of open source solutions for defense and intelligence communities. It discusses how open source software can help address major IT challenges around legacy system integration, data integration, information sharing, certification and accreditation, and software verification. Open source is defined as commercial software and allowed under government policies. Common myths about open source being unsecure, unsupported, or not commercial are addressed. Case studies are presented on how open source can help with problems like system transformation and testing automation. Insider threats are identified as a key cybersecurity risk that open source may help mitigate.