  The twist-three distributions $g_2(x)$ and $h_2(x)$ are defined as
quark-field matrix elements between polarized hadron states. They can be
written in terms of quark-mass and gluonic operators, after which the
Burkhardt-Cottingham sum rule for $g_2$ can be derived and a similar sum rule
for $h_2$. Their role in the Drell-Yan double-spin asymmetry $A_{LT}$ is
explained.
