We explore the embedding of Spin groups of arbitrary dimension and signature
into simple superalgebras in the case of extended supersymmetry. The
R-symmetry, which generically is not compact, can be chosen compact for all the
cases that are congruent mod 8 to the physical conformal algebra so(D−2,2),
D≥3. An so(1,1) grading of the superalgebra is found in all cases.
Central extensions of super translation algebras are studied in this framework.Comment: AMS LaTeX, 16 page