Elastic properties. The tuning of mechanical properties of framework materials is an important research subject, both for their fundamental understanding but also as a crucial property in their potential applications. When it comes to the identification of anomalous elastic properties, such as negative linear compressibility (NLC) or negative Poisson's ratio (auxeticity), the determination of the materials' mechanical behavior is often achieved by a complement of in situ X-ray diffraction experiments, establishing the macroscopic behavior, and computational modeling of the structure and its evolution under stress, allowing for the determination of a microscopic mechanism. Two recent studies exemplify this search for anomalous elastic properties and their understanding. Giri et al. looked at the mechanical behavior of thermally conductive stacks of twodimensional covalent organic frameworks. Through the use of atomistic MD simulations based on the adaptive intermolecular reactive empirical bond order (AIREBO) potential, they showed that a careful engineering of the COF microstructures could lead not only to auxeticity, but to high negative values of the Poisson's ratio -beyond that of other auxetic materials. They could link this behavior to a swiveling motion of the organic linkers under uniaxial tensile strain. In another work, Fan et al. investigated the CALF-20 MOF framework and its mechanical and thermal properties, through a combination of static DFT calculations and constant-pressure MD simulations based on a machine-learned potential. Those revealed that CALF-20 exhibits both negative area compressibility and negative Poisson's ratio in the linear regime, as well as a distinct two-step elastic deformation behavior. That phase transition is induced by strain-softening and is linked to a reorientation of the oxalate ligands of the framework. This study demonstrates that the elastic characterization of MOFs can be a rich tool, even beyond the routine studies of the linear regime.