  This thesis is roughly organized into two parts. The first one (the first
three chapters), expository in nature, attempts to place the current work in
context: at first historically, but then focusing on the Lax formalism and the
Adler--Gel'fand--Dickey scheme for hierarchies of the KdV type. The second part
(the last four chapters) comprises the main body of this work. It begins by
developing the supersymmetric Lax formalism, introducing the ring of formal
superpseudodifferential operators and the associated Poisson structures. We
discuss three supersymmetric extensions of the KP hierarchy (MRSKP, \SKP2, and
JSKP). We define and compute their additional symmetries and we find that the
algebra of additional symmetries are in all three cases isomorphic to the Lie
algebra of superdifferential operators. We discuss a new reduction of \SKP2 and
the relation between MRSKP and \SKP2 is clarified. Finally we consider the (so
far) only integrable hierarchy to have played a role in noncritical superstring
theory (sKdV-B). We identify it, prove its bihamiltonian integrability, and
extend it by odd flows. We close with a discussion of new integrable
supersymmetrizations of the KdV-like hierarchies suggested by the study of
sKdV-B. (This is the author's PhD Thesis from the Physics Deparment of the
University of Bonn, July 1994.)
