  By analogy with the Landau-Ginzburg theory of ordinary zero-form symmetries,
we introduce and develop a Landau-Ginzburg theory of one-form global
symmetries, which we call mean string field theory. The basic dynamical
variable is a string field -- defined on the space of closed loops -- that can
be used to describe the creation, annihilation, and condensation of effective
strings. Like its zero-form cousin, the mean string field theory provides a
useful picture of the phase diagram of broken and unbroken phases. We provide a
transparent derivation of the area law for charged line operators in the
unbroken phase and describe the dynamics of gapless Goldstone modes in the
broken phase. The framework also provides a theory of topological defects of
the broken phase and a description of the phase transition that should be valid
above an upper critical dimension, which we discuss. We also discuss general
consequences of emergent one-form symmetries at zero and finite temperature.
