An organizational strategy to develop software has recently appeared in the market. Organizations release software source code open and hope to attract volunteers to improve their applications, forming what we call an open source project. Examples of organizations that have used this strategy include IBM (Eclipse), Google (Android) and Mozilla (Thunderbird). This phenomenon deserves attention for its usefulness to public and private organizations on saving costs and improving software services to the population. This book theoretically specifies and empirically tests a structural-causal model to explain how projects are populated and operate, consequently, impacting the qualities of the software produced and support provided by the project members. Specific advices to managers engaged in such strategies are provided.