  Let $N_{g}$ denote the closed non-orientable surface of genus $g$ and let
${\mathcal M} _g$ denote the mapping class group of $N_{g}$. Let ${\mathcal T}
_g$ denote the twist subgroup of ${\mathcal M} _g$ which is the subgroup of
${\mathcal M} _g$ is generated by all Dehn twists. In this thesis, we proved
that ${\mathcal T} _g$ is generated by six involutions for $g \geq 16$ or $g =
14$.
