Reparametrizations in String Field Theory.

String theory has recently been recognized as a viable model for the unification of the fundamental forces in nature. Of particular importance is the fact that closed strings contain the graviton as part of their spectrum and could therefore provide us with a consistent quantum theory of gravity. String field theory is a natural arena to examine the dynamics of strings. After the formulation of a gauge-covariant free closed string field theory, an algebraic approach to string field theory based on reparametrization invariance is discussed. The basic formalism of the algebraic approach is that of the Marshall-Ramond formulation of string field theory, where strings are studied as one-dimensional spacelike surfaces evolving in time. The formalism is extended to include the bosonized ghost field, yielding an anomaly -free algebra in the process. The analysis is extended to superstrings and representations of the super-reparametrization algebra are detailed. Invariant operators are constructed from the coordinates and the ghost fields. It is shown that these operators obey an anomalous algebra. In particular, the BRST operator is recovered as the trace of a symmetric spacetime tensor. Alternative representations of the superconformal ghost algebra are considered, leading to supersymmetric bosonization formulae. Dynamical invariants besides the BRST operator are shown to exist in the superbosonized theory.