  Thermal superspace is characterized by Grassmann variables which are
time-dependent and antiperiodic in imaginary time, with a period given by the
inverse temperature. The thermal superspace approach allows to define thermal
superfields obeying consistent boundary conditions and to formulate a
``super-KMS'' condition for superfield propagators. Upon constructing thermal
covariantizations of the superspace derivative operators, we define thermal
covariant derivatives and provide a definition of thermal chiral and antichiral
superfields. Thermal covariantizations of the generators of the
super-Poincar\'e algebra are also constructed, and the thermal supersymmetry
algebra is computed; it has the same structure as at T=0. We then investigate
realizations of this thermal supersymmetry algebra on systems of thermal
fields. In doing so, we observe thermal supersymmetry breaking in terms of the
lifting of the mass degeneracy, and of the non-invariance of the thermal
action.
