  While isolated neutron stars (INSs) are among the brightest gamma-ray
sources, they are among the faintest ones in the optical, and their study is a
challenging task which require the most powerful telescopes. HST has lead
neutron star optical astronomy yielding nearly all the identifications achieved
since the early 1990s. Here, the major HST contributions in the optical studies
of INSs and their relevance for neutron stars' astronomy are reviewed.
