This SpringerBrief discusses multiple forms of open-source-inspired outsourcing: opensourcing, innersourcing and crowdsourcing. It uses a framework-based comparison to explain the strengths and weaknesses of each approach. By pointing out characteristics along with benefits and pitfalls of each approach, the authors provide nuanced and research-based advice to managers and developers facing software sourcing decisions. The differences and commonalities of these three emerging approaches are carefully analyzed. Chapters explore the primary challenges of reliability, efficiency and robustness in open-source methods. Examples from industrial cases are included, along with extensive references to recent research. The brief concludes with a comparative analysis of approaches and outlines key implications to be aware of when outsourcing. Software Sourcing in the Age of Open: Leveraging the Unknown Workforce is designed for professionals and researchers interested in outsourcing challenges. The content is also suitable for postgraduate students interested in contemporary software sourcing approaches.