Abstract
We identify the gauge invariances of the linearized field theory of strings which give rise to the Yang-Mills and general coordinate invariance of this theory. We construct a kinetic energy term for string fields which is invariant to these gauge symmetries. By gauge-fixing, we derive from this action the expressions for the free string action, in particular gauges found by Kaku and Kikkawa and by Siegel. The structure of Stueckelberg auxilliary fields required to make the gauge-invariant action local is rather intricate; to clarify this structure, we develop a theory of differential forms on the space of strings. We conclude with some remarks on the origin of the dilaton and the appearance in the superstring of local supersymmetry.