Significance Light-sheet fluorescence microscopy (LSFM) is an imaging modality in which a sample is illuminated from the side by a beam engineered into a wide and relatively thin “sheet.” This allows highly parallelized planewise scanning of volumes with inherent optical sectioning, offering a good balance between spatial and temporal resolution with reduced photostress. Unfortunately, the axial extent of the illuminated section is ultimately limited by diffraction. Here, we show that a RESOLFT [reversible saturable/switchable optical (fluorescence) transitions] strategy neutralizes the resolution-limiting role of diffraction in LSFM. While other LS strategies exist, which run into new hard axial limits of resolution, LS-RESOLFT is conceptually diffraction-unlimited and can be developed toward molecular-scale resolution.