Software contributions to the reliability of systems of systems Systems of great complexity that require high levels of reliability are increasingly foundational to national security as well as economic and social activities. Many of these systems are in fact systems of systems – an arrangement in which independent and separately useful systems are integrated into a larger functioning system to deliver unique capabilities. Systems of systems depend on the proper functioning of both the constituent systems and the coordination that software can provide to assure reliable accomplishment of a given mission. Software that not only provides the logic for much of the capability of the individual systems but – in bridging between constituent systems with data and control flows – it is may also be leveraged to coordinate and direct the assembled system of systems. This paper will address how software and systems engineering can be key to ensuring that an assembled system of systems accomplishes its mission.