Abstract: Two-dimensional covalent organic framework nanosheets (2D CONs) feature ultrathin thickness and exceptionally high specific surface areas, which can provide efficient transport pathways for charge carriers—including electrons, holes, and ions—through their conjugated backbones and open channels, making them promising candidates for applications in energy storage, photocatalysis, and electrocatalysis. In this review, we first present a comprehensive overview of two typical synthetic strategies for 2D CONs: the top-down approach, and the bottom-up approach. Subsequently, the recent progress of 2D CONs in a series of applications, including photocatalysis, electrocatalysis, energy storage, photoluminescence sensors, environmental remediation and so forth, is summarized. Finally, the current challenges and future directions in this rapidly evolving field are discussed.