Recently, background-independent open-string field theory has been for
mally defined in the space of all two-dimensional world-sheet theories
. In this paper, to make the construction more concrete, I compute the
action for an off-shell tachyon field of a certain simple type. From
the computation it emerges that, although the string field action does
not coincide with the world-sheet (matter) partition function in gene
ral, these functions do coincide on shell. This can be demonstrated in
general, as long as matter and ghosts are decoupled.