FBL18 (F-box and leucine-rich repeat protein 18), also known as FBXL18, is an 805 amino acid protein that contains an F-box near its N-terminus, followed by several leucine-rich repeats and a transmembrane domain at the C-terminus. F-box proteins are critical components of the SCF (Skp1-CUL-1-F-box protein) type E3 ubiquitin ligase complex and are involved in substrate recognition and recruitment for ubiquitination. They are members of a larger family of proteins that are involved in the regulation of a wide variety of cellular processes (including the cell cycle, immune response, signaling cascades and developmental processes) through the targeting of proteins, such as cyclins and cyclin-dependent kinase inhibitors (CDKNs), for degradation by the proteasome after ubiquitination. FBL18 directly interacts with SKP1A p19 and CUL-1, forming a substrate-recognition component of the SCF-type E3 ubiquitin ligase complex. Four isoforms of FBL18 exist due to alternative splicing.