BUECHLER Title: Designing interactions in polar molecules: towards novel quantum phases Abstract: We study quantum degenerate polar molecules with large dipole moments. We show that the internal structure of the polar molecules allows us to tune and shape the long-range part of the interaction: we focus on a pure dipole-dipole interaction, and a hard-sphere type interaction. The strength of the long-range interaction easily exceeds the kinetic energy of the gas. Then, the stability of the system is guaranteed by a strong transverse trapping potential confining the particles into two-dimensional planes. For typical experimental parameters, we find the the ground state is characterized by a crystalline phase, separated from the superfluid phase via a quantum phase transition for a critical interaction strength.