The controlled assembly of metal centres and multitopic organic linkers has been used to great effect in the synthesis of metal-organic nanosheets (MONs) as a versatile class of two-dimensional (2D) materials. In contrast to other 2D materials, MONs possess readily tuneable surfaces with high external surface area and greater concentration of accessible active sites which makes them ideal candidates for applications in the fields of catalysis, sensing, optoelectronics, and separation. In particular, Zr-based MONs (and their Hf analogues) are of great interest due to their stability under harsh thermal and chemical environments. The high surface area of the nanosheets, the Lewis and Brønsted acidities of the Zr clusters, and the ability to post-synthetically functionalise the surfaces through modulator exchange, have enabled their use in promoting thermocatalytic, 9 photocatalytic, and electrocatalytic reactions. Combining Zr 4+ (and/or Hf 4+ ) with ditopic carboxylate ligands typically results in threedimensional metal-organic frameworks (MOFs) rather than MONs. For example, the combination of benzene-1,4-dicarboxylate (BDC) with Zr 4+ can result in: the fcu topology UiO-66, connected by Zr6 clusters; a related polymorph with hex topology; an hcp analogue connected by Zr12 clusters (Figure ); and MIL-140A, which has an infinite one-dimensional chain secondary building unit (SBU). Isolation of 2D phases can be achieved through conversion -either spontaneous or mechanochemically induced -of the hcp phase materials into layered, hxl topology MOFs (Figure ) that can be exfoliated into hns topology nanosheets (limited examples can be prepared directly). This means that the preponderance of Zr MONs reported with linear dicarboxylates contain Zr12 clusters.