The Computational 2D Materials Database (C2DB) is a comprehensive database containing properties of over 1500 two-dimensional (2D) materials across more than 30 crystal structures. It systematically calculates structural, thermodynamic, elastic, electronic, magnetic, and optical properties using density functional theory (DFT) and many-body perturbation theory (G0W0 and Bethe-Salpeter Equation) for around 250 materials. The database is fully open and accessible online, providing a platform for computational modeling and design of new 2D materials and van der Waals heterostructures. The C2DB includes a wide range of properties, such as band structures, effective masses, work functions, and optical absorbance, and is designed to facilitate the discovery of new 2D materials with potential applications in spintronics, (opto-)electronics, and plasmonics. The database is built using a semi-automated workflow, ensuring consistency and transparency in data generation. It includes over 350 materials in the most stable category, with many of them being potentially synthesisable. The database also provides a stability scale to quantify the dynamic and thermodynamic stability of materials. The workflow involves structure relaxation, crystal structure classification, thermodynamic stability assessment, phonon and dynamic stability analysis, elastic constants, magnetic anisotropy, projected density of states, and band structures. The database is built using the GPAW code with plane wave basis sets and PAW potentials, and is managed using the Atomic Simulation Environment (ASE). The database includes a variety of properties, such as band gaps, effective masses, magnetic properties, and plasmon dispersion relations, and is used to identify new materials with tailored properties. The C2DB is a valuable resource for researchers in the field of 2D materials, providing a comprehensive and accessible overview of the rapidly expanding family of 2D materials.The Computational 2D Materials Database (C2DB) is a comprehensive database containing properties of over 1500 two-dimensional (2D) materials across more than 30 crystal structures. It systematically calculates structural, thermodynamic, elastic, electronic, magnetic, and optical properties using density functional theory (DFT) and many-body perturbation theory (G0W0 and Bethe-Salpeter Equation) for around 250 materials. The database is fully open and accessible online, providing a platform for computational modeling and design of new 2D materials and van der Waals heterostructures. The C2DB includes a wide range of properties, such as band structures, effective masses, work functions, and optical absorbance, and is designed to facilitate the discovery of new 2D materials with potential applications in spintronics, (opto-)electronics, and plasmonics. The database is built using a semi-automated workflow, ensuring consistency and transparency in data generation. It includes over 350 materials in the most stable category, with many of them being potentially synthesisable. The database also provides a stability scale to quantify the dynamic and thermodynamic stability of materials. The workflow involves structure relaxation, crystal structure classification, thermodynamic stability assessment, phonon and dynamic stability analysis, elastic constants, magnetic anisotropy, projected density of states, and band structures. The database is built using the GPAW code with plane wave basis sets and PAW potentials, and is managed using the Atomic Simulation Environment (ASE). The database includes a variety of properties, such as band gaps, effective masses, magnetic properties, and plasmon dispersion relations, and is used to identify new materials with tailored properties. The C2DB is a valuable resource for researchers in the field of 2D materials, providing a comprehensive and accessible overview of the rapidly expanding family of 2D materials.