 Like the philosophy of science in general, the philosophy of biology has traditionally been mostly concerned with theories. For a variety of reasons, the theory that has by far attracted the most interest is evolutionary theory. There was a period in the philosophy of biology when this field was almost identical with the philosophy of evolutionary theory, especially if debates on the nature of species are included in this area. From the 1960s almost until the 1990s, basically the only non-evolutionary topic discussed was the issue of the reduction (or non-reduction) of classical genetics to molecular genetics. In the 1990s, practitioners of the field finally started to move into other areas of biology such as cell biology, molecular biology, immunology, neuroscience, as well as addressing philosophical issues other than theory reduction (e.g., Darden 1991; Burian 1992, 1997; Schaffner 1993; Bechtel and Richardson 1993; Rheinberger 1997). As these are profoundly experimental disciplines, an increased attention to the experiment in biology was inevitable. Thus, what is generally known as the “New Experimentalism” in general philosophy of science arose more or less independently in the philosophy of biology, even though this fact has not been advertised much. Perhaps, the increased focus on experimentation was more due to the influence of historians of biology and their practical turn than due to the “New Experimentalists” in general philosophy of science such as Hacking (1983), Franklin (1986) or Mayo (1996). At any rate, today there is a wealth of historical as well as philosophical scholarship that closely studies what goes on in biological laboratories. Some of this literature relates to classical issues in philosophy of science, but it has also explored new philosophical ground.