Conformable phase masks, transparent photopolymers and two photon effects provide the basis for a simple, parallel lithographic technique that can form complex, but well defined three-dimensional (3D) nanostructures in a single exposure step. This paper describes the method, presents examples of its ability to form 3D nanostructures (including freestanding particles with controlled shapes) and comprehensive modeling of the associated optics. Single step, large area 3D pattern definition, subwavelength resolution and experimental simplicity represent features that make this method potentially useful for applications in photonics, biotechnology and other areas.