This paper presents the discovery of free-standing, strictly two-dimensional (2D) atomic crystals, which can be viewed as individual atomic planes pulled from bulk crystals or as unrolled single-wall nanotubes. Using micromechanical cleavage, the researchers prepared and studied various 2D crystals, including single layers of boron nitride, graphite, dichalcogenides, and complex oxides. These atomically thin sheets are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale. Dimensionality is a key material parameter, and 2D crystals are rare among experimentally known materials. The researchers developed a cleavage technique that allows the isolation and study of individual atomic layers from strongly layered materials. This method involves rubbing a fresh surface of a layered crystal against another surface, leaving behind flakes that can be identified under an optical microscope. The technique is simple and effective, allowing the identification of single-layer crystals. The study also includes the characterization of various 2D materials using scanning tunneling, scanning electron, and high-resolution transmission electron microscopy. These studies confirmed that the 2D crystallites remained monocrystalline and showed no degradation over several weeks. The electrical conductivity of the 2D materials was also investigated, revealing that some, like graphene, are metallic and exhibit a pronounced electric field effect, while others, like BN, are highly insulating. The findings demonstrate the existence of 2D atomic crystals that can be prepared by cleavage from most strongly layered materials. These crystals are stable at room temperature and in air, and their high quality and macroscopic continuity make them promising for various applications. The study highlights the potential of 2D crystals for new materials and phenomena, and suggests that they can be grown in large sizes for industrial applications.This paper presents the discovery of free-standing, strictly two-dimensional (2D) atomic crystals, which can be viewed as individual atomic planes pulled from bulk crystals or as unrolled single-wall nanotubes. Using micromechanical cleavage, the researchers prepared and studied various 2D crystals, including single layers of boron nitride, graphite, dichalcogenides, and complex oxides. These atomically thin sheets are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale. Dimensionality is a key material parameter, and 2D crystals are rare among experimentally known materials. The researchers developed a cleavage technique that allows the isolation and study of individual atomic layers from strongly layered materials. This method involves rubbing a fresh surface of a layered crystal against another surface, leaving behind flakes that can be identified under an optical microscope. The technique is simple and effective, allowing the identification of single-layer crystals. The study also includes the characterization of various 2D materials using scanning tunneling, scanning electron, and high-resolution transmission electron microscopy. These studies confirmed that the 2D crystallites remained monocrystalline and showed no degradation over several weeks. The electrical conductivity of the 2D materials was also investigated, revealing that some, like graphene, are metallic and exhibit a pronounced electric field effect, while others, like BN, are highly insulating. The findings demonstrate the existence of 2D atomic crystals that can be prepared by cleavage from most strongly layered materials. These crystals are stable at room temperature and in air, and their high quality and macroscopic continuity make them promising for various applications. The study highlights the potential of 2D crystals for new materials and phenomena, and suggests that they can be grown in large sizes for industrial applications.