  We give a pedagogical review of the computation of Gromov-Witten invariants
via localization in 2D gauged linear sigma models. We explain the relationship
between the two-sphere partition function of the theory and the Kahler
potential on the conformal manifold. We show how the Kahler potential can be
assembled from classical, perturbative, and non-perturbative contributions, and
explain how the non-perturbative contributions are related to the Gromov-Witten
invariants of the corresponding Calabi-Yau manifold. We then explain how
localization enables efficient calculation of the two-sphere partition function
and, ultimately, the Gromov-Witten invariants themselves.
