  We propose that a novel deformation of string perturbation theory, involving
non-local interactions between strings, is required to describe the gravity
duals of field theories deformed by multiple-trace operators. The new
perturbative expansion involves a new parameter, which is neither the string
coupling nor the coefficient of a vertex operator on the worldsheet. We explore
some of the properties of this deformation, focusing on a special case where
the deformation in the field theory is exactly marginal.
