Recent philosophy and history of science has seen a surge of interest in the role of concepts in scientific research. Scholars working in this new field focus on scientific concepts, rather than theories, as units of analysis and on the ways in which concepts are formed and used rather than on what they represent. They analyze what has traditionally been called the context of discovery, rather than (or in addition to) the context of justification. And they examine the dynamics of research rather than the status of the finished research results. This volume provides detailed case studies and general analyses to address questions raised by these points, such as: - Can concepts be clearly distinguished from the sets of beliefs we have about their referents? - What - if any - sense can be made of the separation between concepts and theories? - Can we distinguish between empirical and theoretical concepts? - Are there interesting similarities and differences between the role of concepts in the empirical sciences and in mathematics? - What underlying notion of investigative practice could be drawn on to explicate the role of concept in such practice? - From a philosophical point of view, is the distinction between discovery and justification a helpful frame of reference for inquiring into the dynamics of research? - From a historiographical point of view, does a focus on concepts face the danger of falling back into an old-fashioned history of ideas?