  Helium Ion Microcopy (HIM) based on Gas Field Ion Sources (GFIS) represents a
new ultra high resolution microscopy and nano-fabrication technique. It is an
enabling technology that not only provides imagery of conducting as well as
uncoated insulating nano-structures but also allows to create these features.
The latter can be achieved using resists or material removal due to sputtering.
The close to free-form sculpting of structures over several length scales has
been made possible by the extension of the method to other gases such as Neon.
A brief introduction of the underlying physics as well as a broad review of the
applicability of the method is presented in this review.
