Biphenylene is a polycyclic aromatic hydrocarbon (PAH) with a unique structure consisting of two benzene rings fused in a four-membered ring. This non-benzenoid hydrocarbon is a fundamental unit in the study of strained aromatic systems and novel carbon allotropes. Its synthesis and properties have been a subject of significant theoretical and experimental interest in organic chemistry. The primary application of biphenylene lies in materials science, particularly as a precursor or model compound for novel carbon-based materials and organic semiconductors. Its unique electronic structure, arising from the antiaromatic cyclobutadiene ring fused between two benzene rings, makes it a valuable building block for designing materials with specific optoelectronic properties. It serves as a fundamental unit in the synthesis of larger polycyclic aromatic hydrocarbons and graphene nanoribbons with tailored edges and electronic band gaps, which are relevant for organic light-emitting diodes (OLEDs) and field-effect transistors (FETs). While not a commodity chemical, biphenylene is a specialized research chemical. Its high strain energy and reactivity make it a fascinating subject for fundamental studies in physical organic chemistry and a potential synthon for advanced functional materials.