Since the 1970s, astronomers have detected a set of distinct infrared emission bands across diverse astronomical environments, which are widely recognized as signature features of polycyclic aromatic hydrocarbon (PAH). This paper reviews the formation and evolution mechanisms of such interstellar PAHs, mainly covering bottom-up molecular growth pathways such as the hydrogen abstraction-acetylene addition mechanism. It systematically delineates the fundamental vibrational modes corresponding to the characteristic bands at 3.3 μm, 6.2 μm, 7.7 μm, 8.6 μm, 11.2 μm, and 15–20 μm, while elaborating on the effects of molecular edge geometry and heteroatom doping on the peak positions and intensities of these spectral features. Diagnostic methodologies based on band ratio analyses for inferring the ionization states and molecular sizes of PAHs are synthesized, alongside ongoing debates regarding the non-uniqueness of the spectral carriers and the physical-chemical origins of weak far-infrared bands. Finally, the unparalleled advantages of the James Webb Space Telescope (JWST) in infrared imaging spectroscopy are emphasized, providing novel perspectives for advancing our understanding of interstellar organic chemistry.