  We propose a general framework for quantum field theory on the de Sitter
space-time (i.e. for local field theories whose truncated Wightman functions
are not required to vanish). By requiring that the fields satisfy a weak
spectral condition, formulated in terms of the analytic continuation properties
of their Wightman functions, we show that a geodesical observer will detect in
the corresponding ``vacuum'' a blackbody radiation at temperature T=1/(2 \pi
R). We also prove the analogues of the PCT, Reeh-Schlieder and
Bisognano-Wichmann theorems.
