Symposium II, "Ion Beams─New Applications from Mesoscale to Nanoscale," was held at the 2011 MRS Spring Meeting, April 25-29, in San Francisco, California. This symposium welcomed presentations on ion-beam engineering and characterization of materials properties, structure, topography, and functionality, spanning dimensions from the mesoscale to the nanoscale. While the unique capabilities of ion-beam techniques in the diverse emerging fields of nanoscience and nanotechnology are fast becoming critical for many new applications, the flexibility of ion-beam techniques now enables the development of new tools that can integrate tailoring of nanoscale patterns and structures with unique in-situ imaging and analysis. The recent evolution of such instrumentation has energized new programs, both basic and applied, in fast-developing areas ranging over advanced semiconductor integration, information storage, sensors, plasmonics, molecular engineering, biomaterials, and many aspects of the development of alternative energy resources. In a field displaying such rapid evolution on many fronts, it is appropriate for us to pause occasionally and review the overall state of the field, and its emerging opportunities and challenges.