 The last two sections have treated experiments primarily as ways of testing theoretical hypotheses and causal claims, which is where traditional philosophy of science saw their principal role. However, there exists a considerable body of scholarship in the history and philosophy of biology that shows that this does not exhaust the role of experiments in biology. Experimentation, to echo Ian Hacking’s famous slogan, “has a life of its own” (Hacking 1983). Much that goes on in a biological laboratory does not have the goal of testing a preconceived theory. For example, many experiments play an exploratory role, that is, they assist scientists in discovering new phenomena about which they may not yet have any theoretical account or not even any clear ideas. Exploratory experimentation has been investigated in the history and philosophy of physics (Steinle 1997) as well as biology (Burian 1997, 2007; O’Malley 2007; Waters 2007). These studies show that the development of any discipline in experimental biology cannot be understood by focusing on theories and attempts to confirm or refute these theories. Experimental practice is simply not organized around theories, particularly not in biology. If this is so, we must ask in what other terms this practice can be explained or reconstructed. Recent scholarship has focused in particular on two kinds of entities: model organisms and experimental systems.