While an overwhelming majority of biophysical studies on proteins are performed on dilute solutions, there is now a rapidly growing appreciation of the potential effects of intermolecular excluded volume ("crowding") within the highly volume-occupied cellular interior. A semiquantitative picture of crowding effects in vitro, based on simplified models, has been developed. The next steps toward an understanding of crowding effects within cellular environments are challenging but important for proper modeling of protein functions in vivo. This workshop is organized to address these next steps. Among the topics will be the latest results on the microstructures of the various components of the cytoplasm and on the compositions of the various organelles; the in silico modeling and in vitro mimicking of these complex media, and theories of inhomogeneous fluids that have potential applications to cellular environments. The workshop will serve as a catalyst for new breakthroughs in the study of macromolecular crowding.