FABP4, also known as Adipocyte Fatty Acid Binding Protein (A-FABP) or aP2, is a small cytoplasmic protein belonging to the family of fatty acid-binding proteins (FABPs). It is widely expressed in various tissues, including adipose tissue, macrophages, small intestine, heart, and breast, with particularly high levels in adipocytes and macrophages. The primary function of FABP4 is to serve as an intracellular transporter of fatty acids. It facilitates the uptake, transport, and metabolism of fatty acids by binding to long-chain fatty acids (LCFAs) to form stable complexes. These complexes then shuttle the fatty acids to various intracellular compartments such as mitochondria, endoplasmic reticulum, or peroxisomes for processes like β-oxidation, esterification, or phospholipid synthesis. In addition to its role in fatty acid metabolism, FABP4 is also involved in regulating adipocyte differentiation and insulin sensitivity. Moreover, it plays a significant part in inflammatory responses and immune modulation.