Holomorphic N=1 Special Geometry of Open--Closed Type II Strings

We outline a general geometric structure that underlies the N =1 superpotentials of a certain class of flux and brane congurations in type II string compactications on Calabi-Yau threefolds. This \holomorphic N = 1 special geometry" is in many respects comparable to, and in a sense an extension of, the familiar special geometry in N = 2 supersymmetric type II string compactications. It puts the computation of the instanton-corrected superpotential W of the fourdimensional N = 1 string eective action on a very similar footing as the familiar computation of the N = 2 prepotential F via mirror symmetry. In this note we present some of the main ideas and results, while more details as well as some explicit computations will appear in a companion paper.