  Spacetime superalgebras with 64 or less number of real supercharges,
containing the type IIB Poincare superalgebra in (9,1) dimensions and the N=1
Poincare superalgebra in (10,1) are considered. The restriction D<14, and two
distinct possibilities arise: The N=(1,0) superalgebra in (11,3) dimensions,
and the N=(2,0) superalgebra in (10,2) dimensions. Emphasizing the former, we
describe superparticle and super Yang-Mills systems in (11,3) dimensions. We
also propose an N=(2,1) superstring theory in (n,n) dimensions as a possible
origin of super Yang-Mills in (8+n,n) dimensions.
