  The construction of effective field theories describing M-theory compactified
on $S^1/{\bf Z}_2$ is revisited, and new insights into the parameters of the
theory are explained. Particularly, the web of constraints which follow from
supersymmetry and anomaly cancelation is argued to be more rich than previously
understood. In contradistinction to the lore on the subject, a consistent
classical theory describing the coupling of eleven dimensional supergravity to
super Yang-Mills theory constrained to the orbifold fixed points is suggested
to exist.
