Living systems are fundamentally dynamic and adaptive, relying on a constant throughput of energy. They are also, by definition, self-sustaining over the full range of length and time scales. This characteristic combination of constant adaptive flux and emergent persistence requires that the properties of all living systems must, at some level, be cyclical. Consequently, oscillatory dynamics, in which system properties rise and fall in a regular rhythmic fashion, are a central feature of a wide range of biological processes. The scale of biological oscillations covers enormous ranges, from the sub-cellular to the population level, and from milliseconds to years. The current resurgence in interest in interdisciplinary approaches to cell and molecular biology stems in part from the increasing availability of system-wide data on the state of the components of cellular regulatory networks. Alimiting factor in these approaches is often the lack of suitable ways of characterising a.