The notion of a space-time uncertainty principle in string theory is clarif
ied and further developed. The motivation and the derivation of the princip
le are first reviewed in a reasonably self-contained way. It is then shown
that the nonperturbative (Borel summed) high-energy and high-momentum trans
fer behavior of string scattering is consistent with the space-time uncerta
inty principle. It is also shown that, as a consequence of this principle,
string theories in 10 dimensions generically exhibit a characteristic lengt
h scale which is equal to the well-known 11 dimensional Planck length g(s)(
1/3)l(s) of M-theory as the scale at which stringy effects take over the ef
fects of classical supergravity, even without involving D-branes directly.
The implications of the space-time uncertainty relation in connection with
D-branes and black holes are discussed and reinterpreted. Finally, we prese
nt a novel interpretation of the Schild-gauge action for strings from the v
iewpoint of noncommutative geometry. This conforms to the space-time uncert
ainty relation by manifestly exhibiting a noncommutativity of quantised str
ing coordinates between, dominantly, space and time. We also discuss the co
nsistency of the space-time uncertainty relation with S and T dualities.