  Half quantum vortices (HQVs) in superfluid $^3He-A$ have been speculated
since 1976. Two years ago, Yamashita et al reported a very unusual NMR
satellite in the rotating superfluid $^3He-A$ in a parallel plate geometry.
Recently this satellite has been interpreted in terms of HQVs. Also, the strong
flux pinnings in the triplet superconductors $UPt_3, Sr_2RuO_4$ and
$U_{1-x}Th_xBe_{13}$ have been discovered by Mota and her colleagues which are
interpreted in terms of HQVs. We shall first review the bound state spectra
around a single vortex in unconventional superconductors, which provides the
necessary background. In particular, we find the zero modes of the Majorana
fermions in some of triplet superconductors $UPt_3, Sr_2RuO_4$ and $CePt_3Sn$.
Armed with these results we analyze the microscopic aspects of HQVs in $UPt_3$
and $Sr_2RuO_4$. We compute the quasiparticle density of states and the local
magnetic field around HQVs, which should be accessible to scanning tunneling
microscopy (STM), micromagnetometry and neutron scattering below 300 mK.
