  We consider a general N=(2,2) non-linear sigma-model in (2,2) superspace.
Depending on the details of the complex structures involved, an off-shell
description can be given in terms of chiral, twisted chiral and semi-chiral
superfields. Using superspace techniques, we derive the conditions the
potential has to satisfy in order to be ultra-violet finite at one loop. We pay
particular attention to the effects due to the presence of semi-chiral
superfields. A complete description of N=(2,2) strings follows from this.
