2D magnets represent material systems in which magnetic order and topological phase transitions can be observed. Based on these phenomena, novel types of computing architectures and magnetoelectronic devices can be envisaged. Unlike conventional magnetic films, their magnetism is independent of the substrate and interface qualities, and 2D magnetic properties manifest even in formally bulk single crystals. However, 2D magnetism in layered materials is rarely reported often due to weak exchange interactions and magnetic anisotropy, and low magnetic transition temperatures. Here, the electron spin resonance (ESR) properties of a layered antiferromagnetic CrSBr single crystal are reported. The W‐like shape angular dependence of the ESR linewidth provides a signature for room temperature spin–spin correlations and for the XY spin model. By approaching the Néel temperature the arising of …