This chapter discusses the silicon cell paradigm, i.e. the existing systems biology activity of making experiment-based computer replica of parts of biological systems. Now that such mathematical models are accessible to in silico experimentation through the World-Wide Web, a new future has come to biology. Some experimentation can now be done in silico, leading to significant discoveries of new mechanisms of robustness, of new drug targets, as well as to harder validations or falsifications of biological hypotheses. One aspect of this future is the association of such live models into models that simulate larger parts of the human body, up to organs and the whole individual. Reasons to embark on this type of systems biology, as well as some of the challenges that lie ahead, are discussed. It is shown that true silicon cell models are hard to obtain. Shortcut solutions are indicated. One of the major attempts at silicon cell systems biology, in the Manchester Centre for Integrative Systems Biology, is discussed in some detail. Early attempts at higher order, human, silicon cell models are described briefly, one addressing interactions between intracellular compartments and a second trying to deal with interactions between organs.