Summary: Complexity, in Roger Lewin's view, will be the dominant scientific trend of the 1990s, as scientists from many disciplines come together and begin to discover the underlying similarities in their fields. Briefly, complexity theory - which encompasses chaos - holds that at the root of all complex systems lies a few simple rules. It takes the notion of chaos (which states that within seemingly chaotic systems are elements of order) a step further by actually identifying these rules. For example - the rules which govern the behaviour of molecules will parallel those which guide human behaviour. The goal of complexity theory is a grand unification of the life sciences.