FAT1 (FAT atypical cadherin 1) is a large transmembrane protein belonging to the cadherin superfamily, characterized by multiple extracellular cadherin repeats. Initially identified in Drosophila for its role in planar cell polarity, FAT1 has since been implicated in diverse cellular processes, including cell-cell adhesion, actin dynamics, and Hippo signaling pathway regulation. In mammals, FAT1 is expressed in various tissues, particularly during embryonic development, and plays critical roles in tissue morphogenesis, neuronal migration, and wound healing. Dysregulation of FAT1 has been linked to cancers (e.g., glioblastoma, colorectal carcinoma), where it may act as either a tumor suppressor or promoter depending on context, and to developmental disorders. FAT1 antibodies are essential tools for detecting FAT1 expression patterns, studying its molecular interactions, and exploring its pathophysiological roles. These antibodies are widely used in techniques like immunohistochemistry, Western blotting, and immunofluorescence. However, research challenges persist due to FAT1's structural complexity, alternative splicing variants, and context-dependent functions. Recent studies also highlight FAT1's involvement in cell invasion and immune modulation, making it a potential therapeutic target. Validation of FAT1 antibodies remains crucial, as cross-reactivity with other FAT family members can occur. Ongoing research continues to unravel its dual roles in homeostasis and disease.