Cosmic shear surveys are now collecting photometric redshifts of the sources. We analyse how such photometric redshifts can be used to perform a genuine 3D analysis of the shear fields, with enhanced statistical power over conventional shear analysis on the sky. In particular, 3D lensing has the potential to measure accurately the equation of state of Dark Energy, with a possibility of measuring $w$ with an accuracy of a few percent. Like the microwave background, 3D lensing observables are calculable ab initio, and are largely unaffected by complex astrophysical processes which may limit their power. In this context, we review how 3D information from photometric redshifts can reduce a possible physical systematic effect, arising from intrinsic alignments of galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html