The organic-inorganic perovsike (OIP) methylammonium lead iodide, MAPbI3, has been identified as a promising candidate for the development of efficient solid-state solar cells. However, our understanding of the structural response of this material to pressure is woefully lacking, despite the importance of such information for the fabrication of electronic devices. We propose to collect single-crystal high pressure diffraction data on MAPbI3 over the 0-4GPa range on SXD. We believe these data will enable us to determine conclusively the crystal structures of three phases of MAPbI3 that are believed to exist, and to elucidate the phase transition mechanisms that operate in this technologically relevant material. Such information is only accessible via neutron diffraction.