The document discusses challenges and progress toward legal interoperability for open content and public sector information (PSI) licensing. It describes how free/libre open source software (FLOSS) has largely achieved interoperability over 25+ years through efforts like the GPL and agreements on definitions. For open content and PSI, proliferation of licenses initially caused issues, but adoption of Creative Commons licenses and others has increased, though database rights remain a challenge. Key initiatives like CC and Open Knowledge Foundation are working to resolve remaining incompatibilities and reduce unnecessary license proliferation to fully realize the potential of openly licensed content and PSI through interoperability.