Where companies use a large number of systems, care must be taken to ensure that they work together well, and that plans to modify, add or replace systems are checked for impacts on the overall systems estate. Where significant operational change is envisaged (growth, restructuring etc), a plan for the end state and a sequence of managed changes to achieve that state should be planned, rather than reacting to problems or relying on managers in operations to deal with the changes as they arise. We have experience designing and assessing systems architecture for various sizes of operations, from small and medium-sizes operations where it tends to be relatively straightforward, to very large operations where it is frequently an area that requires significant effort.