In this talk I will introduce a comprehensive materials database including electronic, magnetic, and mechanical properties of single-layer two dimensional (2D) compounds. These 2D compounds are identified by data-mining the ICSD database and classified by their plane groups based on 2D symmetry operations. High-symmetry k-points in the first Brillouin zones are assigned for each plane group and full band structures of these 2D materials are evaluated using PBE and HSE06 hybrid functional. These electronic structure data provides a fertile ground for the future discovery of 2D compounds for solar energy conversion, electronics, and optoelectronics. As a benchmark of the power of this database for 2D materials discovery and design, I will present the discovery of novel 2D materials with different functionalities. For instance, 62 2D photocatalysts with optimal band energies, direct band gaps, and small exciton binding energies are predicted or “reidentified” and the correlation between anion species and their electronic structures are revealed. By correlating the electronic structures of host compounds and their surface reaction configurations, a quantitative descriptor for molecule absorption energy is proposed for designing novel 2D electrocatalysts. As another example of the interplay between electronic structure and material property, two classes of semiconducting 2D compounds with unique elastic properties and negative Poisson’s ratio are discovered. The exotic mechanical behavior is found to correlate with the in-plane cation interaction strength. The work was supported as part of the Center for the Computational Design of Functional Layered Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.