  The purpose of this talk is to review some considerations by the present
author on the possible role of a simple space-time uncertainty relation toward
nonperturbative string theory. We first motivate the space-time uncertainty
relation as a simple space-time characterization of the fundamental string
theory. We then argue that the relation captures some of the important aspects
of the short-distance dynamics of D-particles described by the effective super
Yang-Mills matrix quantum mechanics, and also that the recently proposed type
IIB matrix model can be regarded as a possible realization of the space-time
uncertainty principle.
