Interoperability is essential for the effective formation of Joint, Allied or Coalition task forces. Much work has been done in defining levels of interoperability for information systems in the C4ISR area, in particular, the LISI Reference Model. We assert that understanding organisational interoperability is also vital for the effective command and control of these task forces. DSTO has previously developed a Five Layer Model of C2 Support which includes organisational issues. A model of organisational interoperability is proposed in this paper which extends the LISI model into the more abstract layers of C2 Support, that is, the C2 Frameworks, C2 Processes and Information Management areas.