  We construct three dimensional N=1 Chern-Simons theories living on M2 branes
probing Spin(7) cones. We consider Spin(7) manifolds obtained as quotients of
Calabi-Yau four-folds by an anti-holomorphic involution, following a
construction by Joyce. The corresponding Chern-Simons theories can be obtained
from N=2 theories by an orientifolding procedure. These theories are
holographically dual to M theory solutions AdS_4 \times H, where the weak G_2
manifold H is the base of the Spin(7) cone.
