  This paper examines the causal structure of the commutator of two string
fields, in free light-cone string field theory. By treating the commutator as a
distribution on infinite dimensional loop space, it is shown that the
commutator vanishes when $\int d\ss (\delta X(\ss))^2 <0$. Of more direct
physical interest is the commutator of finite mass fields, obtained by smearing
the string fields with appropriate wave functions. This is shown to vanish at
spacelike separations, reproducing the usual point particle field theory
result. The implications of this for the information spreading mechanism
proposed by Susskind to solve the black hole information problem are discussed.
Finally, it is verified that the above conclusions also hold for the
superstring.
