Boron nitride (BN) has been drawing significant interest in environmental applications owing to its distinct properties, such as a large surface area, great chemical/mechanical strength, and abundant structural defects. BN-based membranes have been utilized in various liquid purification/separation applications associated with reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF). A small number of review studies have been published on the environmental applications of BN-based membranes, including water purification and desalination. However, further studies are vital to gain the comprehensive understanding needed to assess the removal/separation mechanisms in BN-based membranes, although existing reviews cover the water desalination, antibacterial performance, and/or energy applications of BN-based membranes. Therefore, in this review, we provide an overview of the various types of BNs (e.g., functionalized BN nanosheets, nanotubes, and nanofibers) incorporated into RO, NF, and UF membranes. Next, we discuss the fabrication and separation performance of various BN-based membranes. In particular, this review focuses on various main factors, namely, the fabrication techniques of BN-based membranes, membrane physicochemical properties, and contaminant properties that affect the transport, separation, and membrane flux during the use of BN-based membrane processes. Finally, prospective study areas are presented briefly.