The aim of this chapter to explore some theoretical aspects of the economics of systems integration (and disintegration) by placing the idea of systems integration within the context of evolutionary economics. We argue that systems integrators (as firms) as systems integration (as a key capability within and across firms) perform a central function as the 'visible hand' of much modern industrial activity, especially in complex product systems. The latter include a significant subset of capital goods such as mobile communication systems, military systems, corporate IT networks, high speed trains, aircraft, intelligent buildings, air traffic control systems and tailored software packages.