Nanostructure fabrication based on charged-particle beams has for many years been assumed to be at or near its limit. However, the fundamental origins of those limits were not well understood. Secondary electron generation and scattering in materials certainly played a role, but the magnitude and resolution limit introduced by that role was not fully quantified. In recent years, however, the advent of improved microscopy methods, resists with excellent image contrast, and analytic tools such as electron-energy-loss spectroscopy have allowed deeper into the single-nanometer-lithography domain. It has, for instance, pointed to volume plasmons as playing a significant role in the exposure process. Helium ions have also been used to realize sub-10-nm-length-scale lithography. The advent of new bright sources for helium ions with sub-nm-dimension probes suggests novel methods of patterning and perhaps direct milling could permit access to the sub-10-nm or even perhaps sub-1-nm length scales in material modification. In this talk, I will discuss some recent results in this field, but also point to open questions that should be addressed if the ultimate capabilities of beam-based fabrication are to be realized.