  We analyze the nature of space-time nonlocality in string theory. After
giving a brief overview on the conjecture of the space-time uncertainty
principle, a (semi-classical) reformulation of string quantum mechanics, in
which the dynamics is represented by the noncommutativity between temporal and
spatial coordinates, is outlined. The formalism is then compared to the
space-time noncommutative field theories associated with nonzero electric
B-fields.
