We investigate the rare decay $\Lambda_b \to \Lambda \gamma$ which receives
both short and long distance contributions. We estimate the long distance
contributions and find them very small. The form factors are obtained
from $\Lambda_c \to \Lambda \ell \bar{\nu}_\ell$ using heavy quark symmetry
and a pole model. The short distance piece opens a window to new physics
and we discuss the sensitivity of $\Lambda_b \to \Lambda \gamma$
to such effects.