Information and Communication Technology (ICT) practitioners are now readily able to create systems of such interconnected complexity that predicting the effects that small changes (such as minor component failures) will have on overall system performance may become very difficult or perhaps impossible. The notion that system-level behaviour "emerges" from parallel nonlinear interaction of multiple components in ways that are difficult or impossible to predict is explored in this document with reference to the UK's ICT investments and assets. We conclude that while it is true that there are currently limits to our ability to understand the ICT systems that we are capable of creating, nevertheless there are ways forward, including new ways of structuring and approaching software engineering, and teaching IT. This 25, 000- word report is a briefing document commissioned by the Foresight Programme within the Office of Science and Technology of the UK Government's Department of Trade and Industry. Its findings are independent of government and do not constitute UK Government policy. Notes: Seth Bullock, School of Computing, University of Leeds, UK 35 Pages