During the past few years, substantial effort has been devoted to developing new experimental techniques capable of delivering atomic-scale information on surfaces and nanoparticles under catalytic reaction conditions. Since the advent of surface science, pioneering experiments under highly idealized conditions have been performed (at very low gas pressures, <10−6 mbar), and idealized model material systems (e.g., single crystals) have been investigated. However, understanding chemical reactions on singlecrystal surfaces close to ultrahigh vacuum does not always enable prediction of the performance of nanoparticles operating at gas pressures near or above atmospheric pressure. Therefore, this MRS Bulletin issue focuses on the capabilities of atomic-scaleresolution, high-gas-pressure- and high-temperature-compatible in situ probes sensitive to the structure, chemical composition, and dynamical properties of nanomaterials. It will be demonstrated how novel in situ techniques enable one to bridge the combined pressure and materials gaps from ultrahigh vacuum to atmospheric pressures and from metal single-crystal surfaces to nanoparticles or oxides.