  We describe, for arbitrary dimensions the construction of a covariant and
supersymmetric constraint for the massless Super Poincare' algebra and we show
that the constraint fixes uniquely the representation of the algebra. For the
case of finite mass and in the absence of central charges we discuss a similar
construction, which generalizes to arbitrary dimensions the concept of the
superspin Casimir. Finally we discuss briefly the modifications introduced by
central charges, both scalar and tensorial.
