The ever increasing demand for high data storage capacity compels the two-photon (2P) excitation based three-dimensional (3D) bit by bit optical data storage system, where the information is recorded as a localized physical or chemical change inside the volume of recording media. Even though the highly confined property of 2P induced optical data storage has led to a higher recording density, it can only reach a theoretical density up to a few Terabytes per disc, which is far below the requirement for the next generation of information storage devices. This book introduces the emerging field of multi-dimensional optical data storage by using the forefront of nanophotonic techniques, which has the potential to revolutionize the information storage and has no theoretical limitation of storage density by employing the physical dimensions of writing beams.