<p>In the last few decades great strides have been made in chemistry at the nanoscale, where the atomic granularity of matter and the exact positions of individual atoms are key determinants of structure and dynamics. Less attention, however, has been paid to the mesoscale—it is at this scale, in the range extending from large molecules (10 nm) through viruses to eukaryotic cells (10 microns), where interesting ensemble effects and the functionality that is critical to macroscopic phenomenon begins to manifest itself and cannot be described by laws on the scale of atoms and molecules alone.</p> <p>To further explore how knowledge about mesoscale phenomena can impact chemical research and development activities and vice versa, the Chemical Sciences Roundtable of the National Research Council convened a workshop on mesoscale chemistry in November 2014. With a focus on the research on chemical phenomena at the mesoscale, participants examined the opportunities that utilizing those behaviors can have for developing new catalysts, adding new functionality to materials, and increasing our understanding of biological and interfacial systems. The workshop also highlighted some of the challenges for analysis and description of mesoscale structures. This report summarizes the presentations and discussion of the workshop.</p>