Open source innovation is a paradigm shift that involves sharing ideas and intellectual property externally rather than keeping them internal. It allows companies to source ideas from outside their organizations. The document discusses why open source innovation is increasingly popular for business model innovation and provides two case studies as examples. The mountain bike industry benefited from open collaboration with customers to develop new product features. Cadbury set up an open innovation team that established external partnerships and sourced over 50% of research projects from public organizations.