  This review was written for the Encyclopedia of Complexity and System Science
(Springer-Verlag, Berlin, 2008), and is intended as a guide to the growing
literature which approaches the phenomena of cell biology from a more
theoretical point of view. We begin with the building blocks of cellular
networks, and proceed toward the different classes of models being explored,
finally discussing the "design principles" which have been suggested for these
systems. Although largely a dispassionate review, we do draw attention to areas
where there seems to be general consensus on ideas that have not been tested
very thoroughly and, more optimistically, to areas where we feel promising
ideas deserve to be more fully explored.
