Companies often find the rigidity of information technology infrastructures a barrier to change. This is increasingly problematic as, faced with high competitive intensity and environmental turbulence, boards and executive teams seek to formulate and execute dynamic strategy. In the absence of a clearly defined, long-term strategic plan, the IT infrastructure platform needs to be designed and managed in concert with organisational design to achieve the degrees of flexibility the executive team most expects to need. The paper combines IT architecture with multivariate theories of organisational fit into an activity that creates a joint architecture of IT and organisation. The distinctive advantage of the approach is that the architecture is harmonised to the increasingly widespread desire to make strategy on the run. Based on a 98 organization study, we describe relevant concepts, roles and practice for achieving an Organisational Architecture.