Two-dimensional (2D) ion conductors have demonstrated significant advantages in applications such as water treatment, bio-medical, catalysis, energy storage and conversion. The confinement structure of 2D ion conductors provides an ideal platform for studying ion-transport behaviors at nano/angstrom-scale. When the size of the 2D channel is less than 100 nm in at least one direction, the size confinement effect and surface charge of the 2D channel can regulate ion flow, creating nanofluidic transport. This surface-charge-controlled ion transport shows many different properties (e.g. ultrahigh ion conductivity and selectivity) from bulk solutions.The nanofluidic ion transport has been observed in biological channels (e.g. transmembrane protein on the cell) and natural layered materials (e.g. vermiculite and mica), and gained extensive research interest. To finely control the structure, research attempts have been made to synthesize artificial 2D ion conductors, which are typically achieved by "top-down" and "bottom-up" methods. These artificial 2D ion conductors are normally restacked 2D materials with extrinsic nanofluidics or lamellar crystal materials with intrinsic nanofluidics. Artificial 2D ion conductors can be categorized into three types, including inorganic (e.g. graphene), organic (e.g. covalent organic frameworks), and organic-inorganic hybrid ion conductors (metal-organic frameworks). The nanofluidics in 2D nanochannels originate from the interactions between ions and surface charge. When the spatial size of nanochannels is comparable to those of solvated ions, the ions can be partially or fully desolvated to separate solvent molecules and ions. When ions transport in the nanofluidic channels, ions with the same charge of surface charge on the inner wall can be repeled by the electrostatic force, which leads to unipolar ion transport with high flux. By contrast, ions with the opposite charge will be attracted to suppress their transport. Such ion transport within 2D nanoconfined spaces can create unusual phenomena that are distinct from bulk solution, including ion gating, ion current rectification, selective ion conduction, and ultrahigh ion flux. This review also summarizes key factors influencing nanofluidic ion transport in 2D ion conductors and strategies for regulation, which can be achieved by adjusting internal interlayer spacing and surface chemistry of 2D materials, as well as external field regulation of the confined space.Benefiting from the studies of nanofluidic mechanisms, the development of 2D ion conductors is rapid in applications where separation and conduction play critical roles. The application can be classified into three types. The first type is the separation of ions and water molecules, which is mainly used for seawater desalination and water purification to promote efficiency and low energy consumption. The second type is the separation of ions with different valences and sizes, which is crucial for ion separation and extraction of high-value elements (e.g. lithium). The third type is accelerating the ion transport of cations or anions, which is one of the keys to determining the rate capabilities in devices for energy conversion (e.g. osmotic energy conversion and photoelectric conversion) and energy storage (e.g. supercapacitors and batteries).Summary and ProspectsAlthough research on nanofluidics and applications of 2D ion conductors has made significant progress in recent years, there are still several critical challenges from theoretical to practical perspectives. The differences in the size, tortuosity and surface chemistry of parallel and perpendicular nanochannels in 2D ion conductors can lead to increased overall resistance. For instance, restacked 2D membranes usually show fast horizontal ion transport but significantly hindered ion transport across the vertically restacked layers of membranes. It is thus interesting to investigate perpendicular 2D nanofluidic channels constructed by using novel materials and fabrication methods, particularly introducing the external fields (e.g. magnetic and electrical) as an optimal fabrication strategy in the future. To enhance the consistency of nanofluidic ion flow, the connection precision of diverse 2D nanochannels may be modified by vertical pre-alignment of 2D nanosheets to minimize the tortuosity. The electrical double layer (EDL) model is critical to drive the nanofluidics. In previous studies of EDL, the ions are usually simplified as point charges. However, in such narrow nanochannels, the size of ions should not be neglected, as it could directly influence the ion distribution in the EDL and hence the interactions to regulate nanofluidics. To gain a deep insight into ion transport behaviours in 2D nanochannels, it is crucial to obtain a precise geometric structure, EDL structure as well as various surface properties, such as roughness, hydrophilicity and the distribution of surface charge. Using advanced characterization methods combined with precise theoretical calculation can provide invaluable insights into how to control nanofluidic ion transport. For instance, combining electrochemical quartz crystal microbalance with density functional theory can effectively monitor the ion transport and mass exchange processes in 2D ion conductors. In-situ Raman spectroscopy could be used to record the surface chemistry of the inner walls of 2D nanochannels during ion transport, which helps to further clarify the mechanism. Moreover, the ultrahigh ionic conductivity of 2D ion conductors presents a promising avenue for boosting new technologies, such as solid-state batteries, but issues related to the stability and compatibility of the interface between 2D ion conductors and electrodes should be addressed. Finally, scaling up the production of 2D ion conductors is vital for real-world applications in various devices.