Polyamide (PA) thin-film composite (TFC) nanofiltration (NF) membranes, which are extensively utilized in seawater desalination and water purification, are limited by the upper bounds of permeability-selectivity. Recently, constructing an interlayer between the porous substrate and the PA layer has been considered a promising approach, as it may resolve the trade-off between permeability and selectivity, which is ubiquitous in NF membranes. The progress in interlayer technology has enabled the precise control of the interfacial polymerization (IP) process, which regulates the structure and performance of TFC NF membranes, resulting in a thin, dense, and defect-free PA selective layer. This review presents a summary of the latest developments in TFC NF membranes based on various interlayer materials. By drawing from existing literature, the structure and performance of new TFC NF membranes using different interlayer materials, such as organic interlayers (polyphenols, ion polymers, polymer organic acids, and other organic materials) and nanomaterial interlayers (nanoparticles, one-dimensional nanomaterials, and two-dimensional nanomaterials), are systematically reviewed and compared. Additionally, this paper proposes the perspectives of interlayer-based TFC NF membranes and the efforts required in the future. This review provides a comprehensive understanding and valuable guidance for the rational design of advanced NF membranes mediated by interlayers for seawater desalination and water purification.